WO2002044287A1

WO2002044287A1 - Multilayer coating

Info

Publication number: WO2002044287A1
Application number: PCT/SE2001/002633
Authority: WO
Inventors: Christian Bigner; Viljam Dunder
Original assignee: Lotrec Ab; DUNDER, Tony
Priority date: 2000-11-28
Filing date: 2001-11-28
Publication date: 2002-06-06
Also published as: AU2002224303A1

Abstract

Multilayer coating which in use is subjected to a gradually proceeding wear or deterioration, such as an antifouling coating on a ship's bottom or an other surface which is intended to be in contact with water, comprising at least two in sequence in the thickness direction, from a substrate surface counted, arranged layers of coating materials, wherein at least two of said layers exhibit from an other of said at least two layers deviating characteristics, such as composition and/or color or other signal characteristics.

Description

Multilayer coating

This invention is related to multilayer coatings. This expression is intended to comprise coatings arranged on a substrate in a sequence on each other in the thickness direction of the coating, i.e. perpendicular to the substrate surface, extending from an innermost layer close to the substrate surface to an outermost layer of the coating in the direction away from the substrate. The multilayer coating may be arranged e.g. on a substrate which is provided with a primer coating under the multilayer coating. The multilayer coating may comprise two, three or more layers with internally essentially unitary or homogenous, but mutually differing characteristics. In case the multilayer coating comprises a large number of layers, produced e.g. by spraying two or more components or constituents with a mutual quantity ratio of said components which is gradually varied during the coating process, an essentially continuous change of one or more characteristics of the coating, such as chemical composition, from its innermost part to its outermost part may be obtained. Furthermore, each separate layer of the coating may consist of two or more sub-layers of identical characteristics, obtained e.g. by applying the identically same coating material in two or more application steps in sequence, such as juxtaposed position, optionally with intermediate drying steps.

Preferably at least two of the layers in the multilayer coating have mutually different chemical and/or physical characteristics in one or more respects, such as color, chemical composition (in other respects), particle size, particle shape, etc.. According to one embodiment of the invention each such layer within the main thickness extension of the coating exhibits characteristics which are different in one or more respects from the characteristics of at least one adjacent such layer

According to one embodiment the invention comprises an antifouling coating, i.e. a coating which counteracts or prevents the growth of organisms on said coating, especially on surfaces which are intended to be maintained in contact with water under conditions which may cause growth of organisms thereon, such as ships' bottoms, boat hulls, pipe lines, etc. Antifouling agents which are preferred according to this invention comprise zinc materials, such as zinc metal, zinc compounds, especially zinc oxide and material which may form zinc oxide in the coating. The zinc oxide antifouling material is preferably of high purity, e.g., containing, based on the weight, at least 95%, at least 98% or at least 99% of ZnO, and has preferably only a low content of poisonous impurities or constituents for which marking according to EEC Directive 67/548/EEC or Supplements is required, such as below 1%, preferably below 0,1% or below 0,01% or 0,001%. The zinc oxide may be produced according to conventional methods, e.g. oxidation of zinc metal or zinc minerals or other zinc compounds, by precipitation from gas or vapor phase, by decomposition of other zinc compounds, e.g. zinc carbonate etc. as is well known by those skilled in the art. The zinc oxide particles used in the coating may also be produced from very finely divided, e.g. colloidal material, and may also comprise additives, especially inert or non-toxic materials. One group of additives or constituents are materials which influence and improve the activity of the zinc oxide when subjected to electromagnetic radiation, especially visible light or daylight, IR or UN radiation or in other ways influence the activity of the zinc oxide material surface or its catalytic activity or is abel to influence or participate in reactions with inorganic or organic materials, such as oxidation or reduction reactions, e.g. with the formation or peroxy compounds, e.g. hydrogen peroxide. Such additives or constituents may be concentrated to the surface of the zinc oxide particles.

According to an embodiment of the invention the coating exhibits a certain degree of permeability to water. Preferably the permeability decreases step by step or continuously from the outermost part of the coating towards the inner parts or layers of the coating. This embodiment may be used in combination with the embodiment in which an outer layer exhibits a maximum antifouling effect after a shorter time of contact with water than an inner layer

The invention comprises according to one embodiment coatings with layers of mutually different "signal characteristics", which make it possible to distinguish between the various layers of the coating with the aid of a suitable means, such as a suitable radiation detector for detecting e.g. radiation, such as electromagnetic radiation, emitted from the layer or constituents thereof. Such detecting means may be the naked eye or the eye provided with suitable radiation filter means, cameras with sensitivity within various wave length ranges, etc. The emitted radiation may result from lighting with visible, such as white or coloured light, or invisible radiation, e.g. IR (infrared) or UN (ultraviolet) radiation, e.g. by reflection thereof or fluorescence. Detection maybe performed with various suitable detectors which are sensitive for the selected wave length ranges of emitted radiation. Such "signal characteristics" may be exhibited by a coating layer covering the entire area of interest or only parts of said area, such as having the shape of particles, dots, patches, lines, interspaced and distributed regularly or irregularly over the area of interest, covering e.g. up to 30%, up to 10%, up to 5% or up to 1% of said area. Optionally the signal characteristics of the coating or parts thereof may be detectable to the naked eye only when viewed at a close distance, e.g. up to 1 meter, at which the color of each separate part can be distinguished, whereas when viewed at larger distance, e.g. 5 meters or above, the separate parts are not visible or together give a color impression which is essentially the same as the colour of the surrounding coating, optionally with a difference as regards lightness or greyishness. In this way wear and deterioration of the coating may be detectable at a close distance without giving the impression of unsightly patch-like color differences of the coating when viewed at a larger distance.

The signal characteristics and other characteristics may also consist of or comprise a release effect, by which the release of an outer layer from an inner layer or optionally the entire coating from a coating substrate is achieved or made easier, e.g. by the effect of a particular solvent, by the effect of penetration of water through an outer layer or from defects in an outer layer, by spraying a liquid under high pressure, by heating, e.g. of a low-melting material or a foaming material, etc.. The invention also comprises the use of such release materials and layers without any other signal characteristics. Such release layers may simplify the partial or complete removal of an outer layer, optionally for renewing removed parts of said outer layer or for exposing the inner layer.

Thus the only difference between the various layers in the multilayer coating may be the color of the various layers, obtained e.g. by the addition of color pigments of different colors or hues or in different quantities or ratios.

The invention also comprises such multilayer coatings with signal characteristics used on substrates which are not intended to be used in contact with water or under other conditions which may cause the objectionable growth of organisms on said substrates, and thus do not need to be antifouling. Such signal, e.g. color, differences between the layers of the coating improves the visibility of possible wear of or damage on the coating, especially when the degree or rate of wear of the coating varies in different areas of the coating, such as wear in patches. Damaged parts of the coating layer or layers may, when detected by the use of the invention, then be restored or repaired before the effect of the coating, such as antifouling effect, is to an objectionable degree lost at the place of wear or deterioration.

An antifouling coating according to the invention comprises normally as the most essential constituents antifouling agent, preferably zinc compound, especially zinc oxide or zinc oxide forming material, and binder material. The binder may be such a material which is conventionally used in antifouling coatings and/or for zinc oxide as a pigment in paints. Examples of binders are such based on polyurethanes- polyepoxides, polysiloxanes, polyacrylates, polyacrylonitriles, polyester resins, alkydes, polyalkydes, polyvinyl materials, polyolefines, polyaromatics, in pure or modified forms, e.g. halogenated, such as partly or completely fluorinated, e.g. perfluorinated polyolefines, and combinations of such materials with each other or with other known and suitable binder materials for coatings, especially antifouling coatings. The binders may be dispersed or distributed or dissolved in polar or non- polar dispersing or vehicle or solvent materials, usually liquids at ambient conditions. Water or water soluble vehicles or solvents may be suitable for latex product binders. Latex products usually also contain viscosity control agents or thickeners, e.g. cellulose based such materials, e.g. in a quantity of up to 5%, frequently at least 1% by weight.

When zinc metal or zinc compounds, especially zinc oxide, are used as antifouling agents in coatings according to this invention, a suitable content, based on the dry weight of the coating or the combined weight of the antifouling agent and the binder, may be at least 20%, at least 30%, at least 40% or at least 50% and higher, e.g. up to 95%, up to 90%, up to 80%, up to 70% or up to 60%. The content of binder, on the same base, may be e.g. at least 3%, at least 5% or at least 10% or higher, and e.g. up to 80%, up to 60% or up to 40%, depending upon the type of binder and the position of the layer in question in the coating. The ready for use coating material usually contains also other additives, in latex materials e.g. dispersing agents, thickening agents, color pigments, preservatives, etc., in a vehicle, such as water or other polar solvents or vehicles. The quantities of such other additives are usually below 10%, e.g. below 5% for each and in total e.g. below 20% , below 10% or below 5%, and may e.g. amount to at least 5% or at least 2%, all based on dry weight. Together with the zinc antifouling agents, such as zinc oxide, may be used also other antifouling agents, preferably in minor amounts or amounts which do not cause objectionable environmental effects.

In a coating according to this invention, in which the binder content increases from the outer part of the coating towards the inner part, e.g. in relation to the combined content of binder and antifouling agent, especially zinc oxide, said outer.inner binder content ratio may be e.g. from 1:1,5 up to 1:5 or above, or e.g. from a value of about 4-15% of binder at the outer part or layer to 10-30% at the inner layer or substrate, such as within a fraction of at least 50% and optionally at most 80% of the coating thickness, and/or with a ZnO content within a part of at least 50% and optionally up to 80% of the coating thickness within the range from at least 20% or at least 30% up to 90%.

The total thickness of the multilayer coating according to the invention may be e.g. at least 25 microns, at least 50 microns or at least 100 microns, and optionally e.g. up to 500 microns, up to 1000 microns or higher.

Usually the coating according to the invention and the layers thereof are applied with a comparatively even thickness within the are extension thereof , e.g. so that the thickness of at least one such layer or of the coating within at least 25%, at least 50% or at least 75% of the area extension of the layer or coating deviates at most 75%, at most 50% or at most 25% from the average thickness of said layer or coating within said area extension. The coating and the layers thereof may, however, be applied with a larger thickness within areas where more severe and rapid wear or deterioration is expected or observed.

The invention also comprises a coating, especially an antifouling coating, having essentially homogenous composition, such as content of antifouling agents, binders, etc., but also including non-homogenous signal characteristics, e.g. as mentioned above, which make it possible to detect wear or attenuation or decay of the coating, in the thickness direction gradually, continuously or step by step, as well as application and use of such coating and materials for providing the coating.

The invention also comprises coating compositions for the coating and coating method according to the invention, including offering, sale and supply thereof. The coating compositions may be provided e.g. in a set or kit comprising two or more different coating compositions having the mutually different characteristics, especially signal characteristics, according to the invention, when applied in sequence on a surface as inner and outer layers resp. Such sets or kits may comprise the different compositions in separate containers packed together in the same package, or offered or sold as suitable for use according to this invention.

Examples . The following examples of the invention are given as illustrations only and are not intended for restricting the scope of the invention.

Example 1.

A ship's bottom, which had been provided with a primer coating, was coated with three in sequence applied layers of antifouling compositions comprising as antifouling agent zinc oxide prepared by the "French method", i.e. from zinc vapor and air oxygen, with a ZnO content of 99,6% by weight, sieve residue (42 microns) of 0,01%, specific surface area of 4 square meters/gram, and a polyurethane based binder as a latex dispersion together with about 3% talc, a cellulose based thickening agent, dispersing agent and water as main constituents. The contents of zinc oxide and binder resp., based on the weight, in the three basic compositions, were:

Composition 1, bottom layer: 45% ZnO and 13% binder, coloured gray with pigment, Composition 2, middle layer: 45% ZnO and 9% binder, coloured yellow with pigment, Composition 3, outer layer: 45% ZnO and 6,5% binder, white color by ZnO pigment

The layers were applied in sequence with a heated fibre roller in a quantity of 1 litre wet volume per 6 square metres of each composition, The coated substrates consisted of test panels, which were kept submerged in sea water at test stations, where the test panels were kept alternating at rest in the water and alternating were subjected to streaming sea water. The test results showed very little fouling for the entire test period. When inspected after a period of time corresponding to a boating season it was observed that the outer layer was somewhat eroded and had partly fallen off. The remaining parts of the outer layer could be removed, leaving the middle layer intact. The middle layer could easily be distinguished from the outer layer by its yellow color. The test was continued, and the middle layer maintained good antifouling activity with simultaneous gradual erosion and fall off. Within those areas where the middle layer was removed entirely the bottom layer gave continued good antifouling activity.

Example 2.

In experiments similar to example 1, wherein the coating because of the shape of the substrate and the distribution of the water streams was subjected to erosive effects of differing strength within various areas of the panel surface, the areas with the most severe erosion could, readily be determined from the color differences of the layers, so that the layers could be repaired and supplemented within said areas, thereby extending the useful life of the coating.

Example 3.

Tests were performed, wherein the three compositions used in Examples 1 and 2 were applied as outermost coatings adjacent each other on the same test panel surface and tested under the same conditions as in Example 1. Composition 3 remained already from the start of the test free from fouling, whereas compositions 1 and 2 only after a certain period of time in the water exhibited full antifouling effect. The test results of Examples 1 and 3 indicate that the outer layer of composition 3 protects the inner layers of compositions 2 and 1 while permitting the intrusion of water to said inner composition layers so that said layers can reach a state in which they can develop full antifouling activity immediately when they come into direct contact with the sea water by removal or fall-off of the adjacent outer layer.

Example 4.

Experiments were performed with coating of a substrate surface by spraying the two main components mentioned in example 1, zinc oxide and polyurethane based binder, by using two of the compositions mentioned in Example 1, composition 1 and composition 3. The compositions were sprayed from a spraying devices with two inlets and mixing nozzle. The relative amounts of materials supplied through the nozzle or nozzles could be selected and gradually varied at will during the coating operation. The weight ratio of said two compositions was during the coating operation gradually and continuously changed from 100% of composition 1 with a weight ratio of 45% zinc oxide and 13% binder at the start, i.e. the bottom of the coating, to 100% of composition 3, i.e. to 45% zinc oxide and 6,5% binder at the surface of the coating, so that the transition between said two compositions was essentially continuous or at least comprised a large number of steps. The coating showed already from the start good activity against fouling, wherein with a gradual decay and erosion of the coating starting from the outer surface, new parts of the coating were continuously exposed to the water, so that the coating maintained good antifouling effect

Example 5.

The experiments of Examples 1 to 4 were repeated with antifouling compositions with various polyurethane, polyepoxide, polysiloxane, polyacrylate, polyacrylnitrile, polyester resin, alkyde and polyvinyl binders dissolved or dispersed in various non-aqueous non-polar and polar solvent and vehicle systems, for preparing coatings of the multi-layer type with characteristics, such as the color and/or the resistance of the coating against erosion and or ablation and other destructive or attenuating effects of the environment, which varied step- wise up to continuously within the coating from one side of the coating to the other. Results similar to those achieved in Examples 1 to 4 were obtained.

Thus, a main purpose of the invention is to provide an object with a coating on a surface thereof, which coating has step-by-step and/or continuously varied characteristics in one or more respects, which vary step-by-step and/or continuously in the thickness direction of the coating, said characteristics preferably consisting of or also comprising the above mentioned signal characteristics, especially color characteristics. A preferred embodiment of the invention comprises an antifouling coating, an object provided with such a coating, an antifouling coating material, especially as a material combination, and a method of applying such a coating on an object.

According to a preferred embodiment the antifouling coating exhibits at the outer surface thereof a high level of its antifouling power in contact with water immediately from the beginning of said contact, whereas the coating at larger distance from the surface, such as 50% or 75% of its thickness or more may have characteristics which cause a delay of the onset of full antifouling power, e.g. with at least one month, or six months, if brought into direct contact with water under the same contact conditions. Simultaneously or alternatively the resistance of the coating against erosion and/or ablation and/or attenuation and/or other destructive effects in contact with water may increase in the thickness direction from the outer surface towards the inner surface of the coating, i.e. closer to the substrate of the coating, e.g. such that the resistance at a distance from the outer surface of 50% or 75% of the thickness is at least 20%, at least 50% or at least 100% higher than the average resistance in the part comprising the outermost 10% or 30% of the thickness of the coating according to the invention. Simultaneously or alternatively the signal characteristics, e.g. the color of the coating may vary step-by-step or continuously in the thickness direction of the coating, preferably so that steps or layers at different distance from the outer surface when viewed together, can be distinguished, e.g. by the naked eye or when viewed through a light filter of suitable color, preferably when viewed in white light or daylight or in a suitably coloured light. According to one embodiment layers which exhibit mutually different and distinguishable characteristics as regards antifouling power and/or erosion or destruction resistance are also provided with characteristic and distinguishably different colors, which make it easier to identify and distinguish layers having different such characteristics.

Claims

Claims.

1. Multilayer coating which in use is subjected to a gradually proceeding wear or deterioration, such as an antifouling coating on a ship's bottom or an other surface which is intended to be in contact with water, comprising at least two in sequence in the thickness direction, from a substrate surface counted, arranged layers of coating materials, wherein at least two of said layers exhibit from an other of said at least two layers deviating characteristics, such as composition and/or color or other signal characteristics

2. A coating according to claim 1, which comprises zinc oxide or a zinc oxide forming material as an antifouling material.

3. A coating according to claim 1 or 2, wherein at least two in sequence arranged layers exhibit mutually different colours, so that the two layers thereby can be distinguished from each other with a naked eye when viewed in a suitable illumination, especially in white light.

4. A coating according to any of claims 1-3 wherein the resistance of the antifouling coating against erosion and wear in contact with water increases in the thickness direction towards the substrate end of the coating within at least a main part of the coating measured in the direction of the thickness, such as by increasing the relative content of binder or by including more of a more resistant binder toward the substrate end of the coating, preferably so that the erosion or wear rate at a plane at a distance of 20% of the coating thickness from the substrate end is at most 75%, preferably 50%, of the corresponding rate at a plane at 20% of the thickness from the outer end of the coating.

5. A coating according to any of claims 1-4 which comprises an antifouling agent selected from the group consisting of zinc metal, zinc oxide and other zinc compounds, preferably in a quantity above 40%, optionally above 60% of the dry weight of the coating, and optionally together with other antifouling agentsA coating composition set which is suited for applying a coating according to any of claims 1-3 on a substrate surface, such as a ship's bottom or an other surface which is intended to be maintained in contact with water, wherein the set comprises at least two separate coating materials, especially in separate containers, which at least two coating materials after application as separate inner and outer layers resp. exhibit mutually different characteristics, such as composition and/or color.

6. A coating composition set which is suited for applying a coating according to any of claims 1-5 on a substrate surface, such as a ship's bottom or an other surface which is intended to be maintained in contact with water, wherein the set comprises at least two separate coating materials, especially in separate containers, which at least two coating materials after application as separate inner and outer layers resp. exhibit mutually different characteristics, such as composition and/or colour.

7. A method for applying and/or maintaining a multiplayer coating according to any of claims 1-6, especially with a coating composition set according to claim 6, which comprises the application on a substrate surface of two or more layers in sequence of coating materials which form coating layers with mutually different characteristics, such as composition and or color, wherein the separate coating layers are optionally applied as two or more sub-layers of identical characteristics.

8. A method according to claim 7, which comprises the application of an antifouling coating on the surface of an object, which is intended to be in contact with water under conditions which may cause fouling of the surface with organisms of plant or animal type, such as algae, barnacles, etc., such as a ship's bottom, which comprises applying onto said surface, in sequence in the thickness direction, two or more layers of antifouling compositions with mutually different chemical or physical characteristics, such as concentration ratio of binder to antifouling agent, or differing colors of different layers, or as a coating with in the thickness direction continuously and essentially uni-directed variation of one or more characteristics of the coating, from the outer end to the substrate end of the coating.

9. A method according to claim 7 or 8 which comprises spraying antifouling material on a surface with a continuous or step-by-step variation to the characteristics, such as chemical and physical characteristics, of the material forming the coating, such as supplying two or more materials with a spraying device to the surface in a mutual ratio, which is varied during the spraying operation.

10. A method according to claim 9, which comprises spraying two or more materials through a device with mixing means, such as mixing nozzles, and varying the mixing ratio between the materials during the spraying operation.