WO2010149729A1

WO2010149729A1 - Surface activation method

Info

Publication number: WO2010149729A1
Application number: PCT/EP2010/058964
Authority: WO
Inventors: Premkumar Jeromerajan; Srikanth Narasimalu
Original assignee: Vestas Wind Systems A/S
Priority date: 2009-06-26
Filing date: 2010-06-24
Publication date: 2010-12-29

Abstract

The present invention relates to methods for the coating of surfaces of fibre-containing composite materials, wherein organo-silane anchoring agents in the presence of mild acidic aqueous solutions are used to coat surfaces to provide a functional polymer surfaces with increased adhesion strength, such as interfacial strength of joints. The invention further provides for fibre-reinforced composite materials, such as laminates produced by the methods of the invention. The fibre-reinforced composite materials produced by methods according to the present invention may be used for the production of wind turbine blades.

Description

SURFACE ACTIVATION METHOD

FIELD OF THE INVENTION

The present invention relates to methods for the coating of surfaces of fibre-containing composite materials. In particular the present invention relates to methods wherein organo- silane anchoring agents are used to coat surfaces to provide functional polymer surfaces with increased adhesion strength, such as interfacial strength of joints. The invention further provides for fibre-reinforced composite materials, such as laminates produced by such methods. The fibre-reinforced composite materials produced by methods according to the present invention may be used for the production of wind turbine blades.

BACKGROUND OF THE INVENTION

Fibre reinforced composite materials, such as fibreglass reinforced polymer composites are well known materials used in many applications, including automotive, marine and building applications. Fibreglass polymer articles are generally prepared by embedding continuous or chopped fibreglass filaments or bundles in a resinous binder such as polyester or epoxy resin, followed by shaping and curing the shaped structure. The fibres e.g. glass fibres serve to reinforce the structure giving rise to articles having improved strength and stress and shear resistance.

Surfaces of such fibre reinforced composite materials may be activated by physical and chemical methods. In this context, activation means that the surface is suitable for further coatings, such as paint or an adhesive. In conventional methods, the surface of a wind turbine (WT) blade is activated using sand blasting method (physical activation), where after the surface is painted.

However, the conventional method of sandblasting does not provide surfaces with good adhesion strength of the coating or with high interfacial strength of laminate structures. Accordingly there is a need for improved methods, wherein structures are provided with improved strength as well as methods that do not have the drawback of environmental pollution and worker safety, that are associated with methods using sandblasting. OBJECT OF THE INVENTION

It is an object of embodiments of the invention to provide fibre-containing composite materials with an activated surface suitable for painting or suitable for coating with an adhesive, wherein there is high interfacial strength between composite material and paint/adhesive. Accordingly, fibre-containing composite materials may be provided with increased strength of the paint or with increased strength in laminate structures, such as in wind turbine blades with improved interfacial strength of joints that are constructed using polyurethane (PU) adhesive and glass fibre reinforced plastics (GRP) laminate. Thus, the methods according to the present invention improve adhesion of composite joint in blades and/or in the nacelle composite cover, etc.

The improved methods according to the invention will provide polymer surfaces with higher adhesion strength, and may also be produced fast and with fewer costs, having fewer impurities, optionally by robotic methods. The fibre-containing composite materials provided with a surface according to the present invention may be used together with another treated fibre, such as glass fibre surface with adhesives and will provide significant improved binding strength, such as binding strength larger than 20 MPa.

Further advantages include higher and more uniform adhesion strength, improved interfacial toughness and fatigue life of bonded assemblies, and no environmental pollution. The safety of workers handling these methods may be significantly increased if sandblasting is omitted. It is envisioned that the improved surface may be made with negligible to no blade weight increase.

The surface activation technology according to the present invention has been developed by the inventors of the present invention using chemical molecules assembly (~10 to 30 nm thick) on the polymer surfaces and will make functional groups tend to bind the coatings, such as PU materials better than with the conventional sandblasting prior to painting.

The surface activation technology may be implemented by spray coating methods, and is very stable even if the fibre-containing composite materials are subjected to thermal cycling or storage at room temperature for longer intervals.

SUMMARY OF THE INVENTION

It has been found by the present inventor(s) that by hydrolyzing an organo silane anchoring agent at low pH and simultaneously or subsequently coating a surface of a fibre-containing composite material with this organo silane anchoring agent, a surface is obtained that has improved ability to bind a subsequent further coating or adhesive.

As hydrolysis enhance the adhesion strength the total binding strength will depend on the total ratio of hydrolysis. It is to be understood that water alone only hydrolyses approximately 50% of the organo silane anchoring agent monomers, whereas diluted acids, such as hydrochloric acid (0.01 M) hydrolyses nearly 100% of organo silane anchoring agent monomers.

In a first broad aspect the present invention relates to a method of preparing an organo silane anchoring agent which is suitable for establishing anhoring materials containing functional chemical groups, as well as compositions comprising a high ratio of hydrolyzed molecular entities, wherein the organo silane anchoring agent is hydrolyzed in an acidic aqueous solution having a pH lower than 3.2.

In a second aspect the present invention relates to a method for the coating of a surface of a fibre-containing composite material with at least one organo silane anchoring agent which method comprises the sequential or simultaneous steps of

a) hydrolyzing the anchoring agent in an acidic aqueous solution having a pH lower than 3.2; and

b) coating the surface with the hydrolyzed anchoring agent.

In a third aspect the present invention relates to a fibre reinforced composite material coated with an organo silane anchoring agent according to methods of the invention.

In a further aspect the present invention relates to a method for the production of an object made of a fibre reinforced composite material which methods comprises the sequential or simultaneous steps of

a) providing an organo silane anchoring agent;

b) hydrolyzing the anchoring agent in an acidic aqueous solution having a pH lower than 3.2;

c) coating a surface of the fibre reinforced composite material with the hydrolyzed anchoring agent; and d) then further coating the coated fibre reinforced composite material obtained under step c) with a paint, adhesive or other suitable surface coating.

In a further aspect the present invention relates to a laminate or interconnected object of fibre reinforced composite material produced according to the methods of the invention.

In a further aspect the present invention relates to a wind turbine blade made by a process according to the invention, or made of a laminate or interconnected objects made according to the invention.

In a further aspect the present invention relates to a wind turbine comprising a turbine blade made by a process according to the invention, or made of a laminate or interconnected objects made according to the invention.

In a further aspect the present invention relates to a method for improving interfacial strength of a joint of two objects made of fibre reinforced composite material, the method comprising a step of providing at least one surface of the joint on one or both objects with at least one organo silane anchoring agent hydrolyzed in an acidic aqueous solution having a pH lower than 3.2.

In a further aspect the present invention relates to a method for improving adhesion of paint or similar coating or adhesive on a fibre reinforced composite material, the method comprising the steps of

a) providing a surface of the fibre reinforced composite material with at least one organo silane anchoring agent hydrolyzed in an acidic aqueous solution having a pH lower than 3.2; and

b) applying the paint or other coating material to the fibre reinforced composite material.

LEGENDS TO THE FIGURE

Fig. 1 shows a schematic view of Surface Activation Technology for a wind turbine blade. GRP refers to glass-fibre reinforced plastic material. In the conventional methods on the left panel, the surface is sandblasted and then painted or supplied with an adhesive. In the new surface activation technology according to the invention, the surface is cleaned and then coated with amino silane anchoring agents before the painting and/or application of adhesive. Fig. 2 illustrates aspects of the Surface Activation. The surface may be treated with atmospheric plasma treatment or flame treatment prior to coating with the amine based silane coupling agent in one or more spray coatings.

Fig. 3 illustrates some suitable amino silanes for the SAT application, 3- aminopropyl)trimethoxysilane and N-(2-aminoethyl)-3-amino-propyltrimethoxy silane. It is illustrated that the methoxygroups are hydrolysed to make easy bond formation with the reactive groups on the fibre reinforced polymer material, which in the figure is a fibreglass reinforced polymer. The amino groups on the amino silane anchoring agent function as anchoring groups for the subsequent coating with paint or adhesive.

Fig. 4 illustrate how hydrolyzed organo silane anchoring molecules make binding with glass fibre, such as WT blade material. The free amino groups provides for a strong binding of adhesives, such as in the binding of another surface treated in the same way, such as in the preparation of laminates or when connecting two objects.

Fig. 5 illustrates the technology without hydrolysis of amino silane anchoring molecules which will provide low binding strength in the range of 5 MPa.

DETAILED DISCLOSURE OF THE INVENTION

As described previously the present invention relates to methods for the coating of a surface of a fibre-containing composite material with at least one organo silane anchoring agent which method comprises the sequential or simultaneous steps of

a) hydrolyzing the anchoring agent in an acidic aqueous solution having a pH lower than 3.2; and b) coating the surface with the hydrolyzed anchoring agent.

The fibres of the fibre-containing composite material may be selected from the group consisting of carbon fibres, polymer fibres, glass fibres, aramid fibres, synthetic fibres, bio fibres, mineral fibres, ceramic fibre metal fibres, boron fibres, and combinations of these.

In some embodiments, the fibrous material includes or consists of glass fibre. Suitable examples of glass fibres may include E-glass or S-glass fibre. In one embodiment, a fibrous material may include a polymer fibre. Suitable examples of fibres may include, but are not limited to, glass fibres (for example, quartz, E-glass, S-2 glass, R-glass from suppliers such as PPG, AGY, St. Gobain, Owens-Corning, or Johns Manville), polyester fibres, polyamide fibres (for example, NYLON polyamide available from E.I. DuPont, Wilmington, Del., USA), aromatic polyamide fibres (such as KEVLAR aromatic polyamide available from E.I. DuPont, Wilmington, Del., USA; or P84.RTM. aromatic polyamide available from Lenzing

Aktiengesellschaft, Austria), polyimide fibres (for example, KAPTON polyimide available from E.I. DuPont, Wilmington, Del., USA), or extended chain polyethylene (for example, SPECTRA polyethylene from Honeywell International Inc., Morristown, NJ., USA; or DYNEEMA polyethylene from Toyobo Co., Ltd.), and the like.

In some embodiment, the fibrous material may include a carbon fibre. Suitable examples of carbon fibres may include, but are not limited to, AS2C, AS4, AS4C, AS4D, AS7, IM6, IM7, IM9, and PV42/850 from Hexcel Corporation; TORAYCA T300, T300J, T400H, T600S, T700S, T700G, T800H, T800S, TlOOOG, M35J, M40J, M46J, M50J, M55J, M60J, M30S, M30G, and M40 from Toray Industries, Inc; HTS12 K/24 K, G30-500 3 K/6 K/12 K, G30-500 12 K, G30- 700 12 K, G30-700 24K F402, G40-800 24K, STS 24K, HTR 40 F22 24K 1550tex from Toho Tenax, Inc; 34-700, 34-700WD, 34-600, 34-600WD, 34-600 Unsized from Grafil inc.; T-300, T-650/35, T-300C, T-650/35C from Cytec Industries.

A particular suitable fibre is glass fibres. Any suitable glass fibre may be used in the method according to the present invention. The term "glass fibres" as used herein means fibres formed by attenuation of one or more streams of molten glass and to strands formed when such glass fibre filaments are gathered together in the forming. The term includes yarns and cords formed by plying and/or twisting a multiplicity of strands together and to woven and non-woven fabrics which are formed of such glass fibre strands, yarns, cords, films or wafers, or may be particulate glass which is used as filler or a catalytic substrate in a number of applications. The invention is particularly applicable to continuous drawn fibreglass fibres (bundles) which are used as reinforcing fibres in the manufacture of polymer bound composites. The present invention is usable with E-type as well as S-type glass-fibres.

The resin of the fibre-containing composite material may be based on unsaturated polyester, polyurethane, polyvinylester, epoxy, thermoplastics, or combinations of these. The resins employed in the practice of this invention are commercially available in solutions which can be simply blended with other components in the preparation of the compositions embodying the features of the present invention. Suitable glass includes silica, alumina, silicate and other oxide glasses.

The methods according to the present invention utilize at least one glass fibre anchoring agent in the form of an organo silicon compound. Preferred for this purpose are functional silane monomers or polymers containing a functional group which can couple with the resinous fibre binder materials. Suitable functional silanes include amino silanes, vinyl silanes, methacryloxy silanes, mercaptosilanes, and epoxy silanes.

Preferred for this purpose are organo silicon compounds which include organo silanes containing one to three hydrolyzable groups, such as halogen (bromine, chlorine, fluorine or iodine) or alkoxy having one to six carbon atoms, such as methoxy, ethoxy, propoxy, butoxy, etc., and containing at least one organic group attached directly to the silicon atom, with any remaining valences on the silicon atom being taken up by hydrogen. Under mild acidic conditions in aqueous solution according to the present invention, such silanes hydrolyze to form the corresponding silanols and/or siloxanes, and hence the anchoring agent is present in the aqueous size composition of the invention as the silane, silanol and/or siloxane.

The organic group or groups attached at the silicon atom may a variety of groups including alkyl having 1-10 carbon atoms, such as methyl, ethyl propyl, hexyl, etc.; alkenyl containing 2-8 carbon atoms, such as vinyl, alkyl, etc.; cycloalkyl having 4-8 carbon atoms, such as cyclopentyl, cyclohexyl, etc.; aryl containing 6-15 carbon atoms, such as phenyl, naphthyl, benzyl, etc. and the halogen, amino, hydroxy, mercapto, glycidoxy or epoxy substituted derivatives thereof. It is to be understood that wherein organo silane contains more than one organic group, the various organic groups attached to the silicon atom can be the same or different from each other.

Representative examples of compounds falling within the above group are ethyldichlorosilane, propyltrichlorosilane, n-butyl-trimethoxysilane, gamma- aminopropyltrimethoxysilane, delta-amino- but ltriethoxysilane, bis(gamma-aminopropyl)di- methoxysilane, delta-aminobutylethyldimethoxysilane, beta-hydroxyethyltriethoxysilane, glycidoxypropyltrimethoxysilane, gamma- chloropropyl-trichlorosilane, vinyldichlorosilane, gamma-a inoallytrimethoxysilane, beta-amino- vinyltriethoxysilane, 3,4- epoxycyclohexyltrimethoxysilane, 3-amino-cyclohexylethyltriethoxysilane, paraaminophenyltriethoxysilane, methacryloxypropyltri- methoxysilane, N-(be a-a inoethyl)- gamma-aminopropyltri- methoxysilane, gamma-mercapropropyltriethoxysilane, gamma- hydropropyltrimethoxysilane, as well as a variety of others. In general, those silanes preferred are those in which at least one group is substituted by at least one amino group.

Examples of such functional silane monomers and polymers thereof, include gamma- aminopropyltrialkoxysilanes, gamma-isocyanatopropyl-triethoxysilane, vinyl -trial koxysilanes, glycidoxypropyltrialkoxysilanes and ureidopropyltrialkoxysilanes, such as A-187 gamma- glycidoxy-propyltrimethoxysilanes, A-174 gamma-methacryloxypropyltrimethoxysilane, A- 1100 gamma-aminopropyl-triethoxysilane, A-1108 amino silane and A-1160 gamma- ureidopropyl-triethoxysilane (each of which are commercially available from OSi Specialties, Inc. of Tarrytown, N.Y.).

Amino silane, monomers and polymers have been found to be particularly effective, e.g. trimethoxysilylpropyidiethylene-triamine, N-methylaminopropyltrimethoxysilane, aminoethylaminopropylmethyidimethoxysilane, aminoethylaminopropyltrimethoxysilane (Dow Corning Z-6020), a homopolymer of an amino silane (Dow Corning Z-6137), aminopropylmethyidimethoxysilane, aminopropyltrimethoxysilane, polymeric aminoalkylsilicone, aminoethylaminoethylaminopropyl-trimethoxysilane, N- methylaminopropyltrimethoxysilane, methylamino-propyltrimethoxysilane, aminopropylmethyidimethoxysilane, aminopropyltriethoxysilane, 4-aminobutyltriethoxysilane, and oligomeric aminoalkylsilane and the like, which are available from Dow Corning, Midland, Mich., Union Carbide Specialty Chemicals Division, Danbury Conn, and HuIs of America, Piscataway, NJ., Wacker Silicones Corporation of Adrian, Mich.

Particularly preferred organo silanes used according to the present invention are (3- aminopropyl)trimethoxysilane, N-(2-aminoethyl)-3-amino-propyltrimethoxy silane (Z-6020, Dow Corning), as well as (3-((2-Aminoethyl)amino)propyl) silanetriol homopolymer (Z-6137, Dow Corning).

Preferably the organo-silane anchoring agents are used in the method according to the present invention in aqueous solutions in an amount of 0.1 to 0.15% of the organo-silane.

However, the organo-silane anchoring agents may be used in the method according to the present invention in aqueous solutions in an amount of 0.1% to 0.5% of the organo-silane, such as in an amount 0.1% to 0.4%, such as in an amount 0.1% to 0.3%, such as in an amount 0.1% to 0.2%, such as in an amount 0.1% to 0.15%.

In some embodiments according to the invention, the fibre reinforced surface is treated prior to the coating with organo-silane anchoring agents. This may include a gentle cleaning as well as chemical and physical treatments, such as oxidizing methods like plasma, corona discharge, and flame activation. When using the above oxidation techniques, the high energy will oxidise the top surface of the composite material and convert chemical groups in the composite material into oxygenated functional groups, such as hydroxyl, carboxyl, and/or carbonyl functional group.

The fibre reinforced polymer surface used according to the present invention may be treated with a plasma treatment, such as when subjecting the fibre surface to ionized gas plasma containing water vapour under conditions such that the water molecules become highly excited, ionized and disassociated. In this condition, the water quickly hydrates the glass surface which it contacts leading to increased hydroxyl group density on the glass surface.

The binding strength may be higher than e.g. 10 MPa, such as higher than 15 MPa, such as higher than 20 MPa between the laminates while using the surface activation. Binding strength means interlocking between the adhesives and the composite panels in terms of physical and mechanical bonding. The strength can be measured by single lap shear tests using universal tensile test equipment.

The resin for the composite material may be provided as liquid, semisolid or solid resin. The resin may be a thermoplastic or a thermosetting resin. The resin may be based on unsaturated polyester, polyurethane, polyvinylester, epoxy, thermoplastics or similar chemical compounds, including combinations of these. In some embodiments of the invention, the resin used in the composite materials according to the present invention is provided as a liquid and the resin has been introduced by Resin Infusion, Resin Transfer Moulding, RTM, or Vacuum Assisted Resin Transfer Moulding, VARTM, into an entity comprising several layers comprising fibres (e.g. fibre tows or any other suitable collection comprising fibres mentioned herein).

The adhesive used according to the present invention may be any tacky material, or a solid with a tacky surface and the adhesive may for example comprise polyester, polyurethane, polyvinylester, epoxy or similar compounds or a combination of these. It is within the scope of the invention to use any material or combination of materials having a tacky surface including solid materials with tacky surfaces. More than one type of adhesive may be used in one member or in the interface of composite joints. For example, it is within the scope of the invention to use the resin as an adhesive between layers of fibre tows, where a resin is provided, or to use a second type of resin below the first layer of fibre tows. A preferred adhesives used according to the present invention is polyurethane.

In some preferred embodiments, the resin is a solid resin. An entity comprising several layers of oriented fibre tows, which may have been immobilised during fibre laying by an adhesive, and a solid resin system is heated under vacuum in order to prepare a pre-consolidated or cured pre-form.

In a further preferred embodiment, the resin is a semisolid and functions both as resin and as adhesive, i.e. during fibre laying, the resin will immobilise the fibres and during subsequent processing, it functions as a matrix material.

The resin may comprise more than one system. It may be advantageous to use more than one resin system to be able to optimise the properties of the resin for the subsequent steps of processing, for example with respect to viscosity and timing/controlling of the curing process. These systems may or may not be based on the same type of resin, however, it is preferred that such systems are based on the same type of resin such as two or more epoxy- based systems. In another preferred embodiment, the resin types differ but the resins are compatible. In a further preferred embodiment, the resin comprises two substantially epoxy- based systems. The two epoxy-based systems may comprise a common component. The common component may for example be a common catalyst, a common amine component or a common epoxy component, however, it is preferred that the common component is an epoxy component. A resin comprising two epoxy-based systems with a common epoxy component may comprise an amine-component of a first epoxy-based system that will react to the common epoxy component.

Besides fibres and resin, composite materials may comprise one or more of fillers (e.g. an inert material) and/or solvents and/or diluents and/or rheological agents and/or viscosity adjusting agents.

The method according to the invention may be adapted to automated processing. For example a robot may advantageously distribute layers comprising fibres, resin, organo silane anchoring agent, and optionally adhesive or paint.

Fibre-containing composite materials and chemical compounds used according to the invention may contain components, which may be irritant or harmful when in contact with naked skin, if ingested or inhaled. Since the processes according to the invention are particularly suited for automation and since avoidance of direct contact is therefore highly desirable, the products and processes according to the present invention represent a significant improvement to the working environment. Definitions

As used herein a "fibre-containing composite material" refers to a composite material comprising fibres together with a resin or plastic, such as epoxy, polyester or vinylester resin. The term is used interchangeably with the term "fibre reinforced composite material". The term includes but is not limited to glass-reinforced plastic as well as other composite materials such as carbon-fibre reinforced plastic.

The term "organo silane anchoring agent" as used herein refers to any organic compound comprising a silicon atom containing one to three hydrolyzable groups, such as halogen (bromine, chlorine, fluorine or iodine) or alkoxy groups having one to six carbon atoms, and containing at least one organic group attached directly to the silicon atom. In some preferred embodiments this organic group attached directly to the silicon atom contain one, two or three free amino groups that may function as anchoring groups with a paint or adhesive coating according to the present invention.

Specific embodiments of the invention

The methods according to the invention will provide/create increased amounts of surface functional groups on the polymeric surface being treated and will tend to cross link with the adhesives and further to composites to get better adhesion strength in terms of physical and covalent chemical bonding between the anchor molecule-adhesives- polymer substrates.

In general, a polymer based composite surface is difficult to wet due to low surface energy. This may lead to poor adhesion with the adhesive and in laminates. To methods according to the present invention changes such behavior to get good binding strength of polymer composite surface with the adhesives. The present method/innovation is one of the surface activation methods which will lead to high surface energy and which will tend to wet the surface in terms of creating surface functional groups.

The methods according to the present invention for coating of a surface of a fibre-containing composite material with at least one organo silane anchoring agent which method comprises a step of hydrolyzing the anchoring agent in an acidic aqueous solution having a pH lower than 3.2.

It is to be understood that the hydrolyzing of the organo silane anchoring agent and the subsequent coating may be performed in the same step. Accordingly, the organo silane anchoring agent may be present and used directly in the coating in the acidic aqueous solution having a pH lower than 3.2. In such an acidic aqueous solution there will be an equilibrium between hydrolyzed compound and non-hydrolyzed with the majority of entities being hydrolyzed. Alternatively the organo silane anchoring agent may be added to the acidic aqueous solution having a pH lower than 3.2 just prior to the coating.

In some embodiments the acidic aqueous solution has a pH lower than 3.0, such as lower than 2.8, such as lower than 2.6, such as lower than 2.4, such as lower than 2.2, such as lower than 2.0, such as lower than 1.8, such as in the range of 1.8 to 3.2, such as in the range of 1.8 to 3.0, such as in the range of 1.8 to 2.8, such as in the range of 1.8 to 2.6, such as in the range of 1.8 to 2.4, such as in the range of 1.8 to 2.2.

In some embodiments the acidic aqueous solution is a solution of an acid selected from acetic acid, formic acid, oxalic acid, nitric acid, sulphuric acid, and hydrochloric acid.

In a preferred embodiment the acidic aqueous solution is a solution of hydrochloric acid.

In some embodiments the acidic aqueous solution is applied to the glass-containing surface in combination with said organo silane glass fibre anchoring agent.

In some embodiments the acidic aqueous solution is applied to said surface of a fibre- containing composite material by spraying.

In some embodiments the organo silane anchoring agent is selected from the group consisting of an organo silane having 1 to 3 readily hydrolyzable groups and containing at least one organic group attached directly to the silicon atom, the corresponding silanes, silanols and/or polysiloxanes.

In some embodiments the organo silane anchoring agent has 3 readily hydrolyzable groups, such as identical hydrolyzable groups.

In some embodiments the organo silane anchoring agent is an aminosilane represented by the formula OR¹

R⁴O Si - R^z

OR^J

wherein R¹, R³ and R⁴ is a hydrocarbon group and R² is an amino-substituted alkyl radical wherein the alkyl groups have from 1 to 6 carbon atoms.

It is to be understood that R¹, R³ and R⁴ are hydrocarbon groups that may or may not be the identical groups. In a preferred embodiment, two or three of the groups are identical.

In some embodiments the organo silane anchoring agent is an aminosilane represented by the formula

OR¹

R^₀ Si R'

OR¹

wherein R¹ is a hydrocarbon group and R² is an amino-substituted alkyl radical wherein the alkyl groups have from 1 to 6 carbon atoms.

In some embodiments R² is an amino-substituted alkyl radical with one amino group. In some embodiments R² is an amino-substituted alkyl radical with two amino groups. In some embodiments R² is an amino-substituted alkyl radical with three amino groups.

In some embodiments the organo silane anchoring agent is selected from the group consisting of (3-aminopropyl)trimethoxysilane, N-(2-aminoethyl)-3-amino-propyltrimethoxy silane, and 3-amino-propyltriethoxysilane. In some embodiments the surface of a fibre-containing composite material is a glass fibre reinforced plastic surface.

In some embodiments the surface of a fibre-containing composite material is a carbon fibre reinforced plastic surface.

In some embodiments the fibre-containing composite material is an epoxy/glass fibre composite material.

In some embodiments the fibre-containing composite material is an epoxy/carbon fibre composite material.

In some embodiments the method further comprises a step prior to said step a) of subjecting said surface of a fibre-containing composite material to a plasma gas treatment and/or flame treatment in order to etch the surface and/or to increase the amount of functional groups, such as hydroxyl, carbonyl, or carboxyl groups on said surface.

In some embodiments the organo silane anchoring agent is used in aqueous solution, wherein the organo silane anchoring agent is present in an amount up to 0.5%, such up to 0.4%, such as up to 0.3%, such as up to 0.15%, such as in the range of 0.1% to 0.15%.

In some embodiments the coating provides a functional layer on the surface of said fibre- containing composite material with a thickness of 10-30 nm.

In some embodiments at least two objects made of fibre reinforced composite material according to the present invention and further coated with an adhesive are bound together on the surface of the coatings.

In some embodiments the adhesive is a polyurethane adhesive.

In some embodiments the object made of glass fibre reinforced composite material is a wind turbine blade.

In some embodiments the laminate or interconnected object prepared according to the present invention has a binding strength between laminate or interconnected objects higher than 10 MPa, such as higher than 12, such as higher than 14 MPa, such as higher than 16 MPa, such as higher than 18 MPa, such as higher than 20 MPa, as measured by single lap shear tests using universal tensile test equipment. EXAMPLE 1

Commerically available amino silane (3-aminopropyl trimethoxysilane or N-(2-aminoethyl)-3- amino-propyltrimethoxy silane) is diluted into 0.1 to 0.15% and then add 0.01 M diluted hydrochloric acid and mixed properly and stored in room temperature. After 15-20 minutes, the solution is ready for spray for the surface activation of an epoxy/glass fibre reinforced plastic surface.

Claims

1. Method for the coating of a surface of a fibre-containing composite material with at least one organo silane anchoring agent which method comprises the sequential or simultaneous steps of

a) hydrolyzing said anchoring agent in an acidic aqueous solution having a pH lower than 3.2; and b) coating said surface with the hydrolyzed anchoring agent.

2. The method according to claim 1, wherein said acidic aqueous solution has a pH lower than 3.0, such as lower than 2.8, such as lower than 2.6, such as lower than 2.4, such as lower than 2.2, such as lower than 2.0, such as lower than 1.8, such as in the range of 1.8 to 3.2, such as in the range of 1.8 to 3.0, such as in the range of 1.8 to 2.8, such as in the range of 1.8 to 2.6, such as in the range of 1.8 to 2.4, such as in the range of 1.8 to 2.2.

3. The method according to claim 1 or 2, wherein said acidic aqueous solution is a solution of an acid selected from acetic acid, formic acid, oxalic acid, nitric acid, sulphuric acid, and hydrochloric acid.

4. The method according to any one of claims 1-3, wherein said acidic aqueous solution is applied to the glass-containing surface in combination with said organo silane glass fibre anchoring agent.

5. The method according to any one of claims 1-4, wherein said acidic aqueous solution is applied to said surface of a fibre-containing composite material by spraying.

6. The method according to any one of claims 1-5, wherein said organo silane anchoring agent is selected from the group consisting of an organo silane having 1 to 3 readily hydrolyzable groups and containing at least one organic group attached directly to the silicon atom, the corresponding silanes, silanols and/or polysiloxanes.

7. The method according to any one of claims 1-6, wherein said organo silane anchoring agent is an aminosilane represented by the formula OR¹

R¹O Si - R^z

OR¹

8. The method according to any one of claims 1-7, wherein said organo silane anchoring agent is selected from the group consisting of (3-aminopropyl)trimethoxysilane, N-(2- aminoethyl)-3-amino-propyltrimethoxy silane, and 3-amino-propyltriethoxysilane.

9. The method according to any one of claims 1-8, wherein said surface of a fibre- containing composite material is a glass fibre reinforced plastic surface.

10. The method according to any one of claims 1-9, wherein said fibre-containing composite material is an epoxy/glass fibre composite material.

11. The method according to any one of claims 1-10, wherein said method further comprises a step prior to said step a) of subjecting said surface of a fibre-containing composite material to a plasma gas treatment and/or flame treatment in order to etch the surface and/or to increase the amount of functional groups, such as hydroxyl groups on said surface.

12. The method according to any one of claims 1-11, wherein said organo silane anchoring agent is used in aqueous solution, wherein the organo silane anchoring agent is present in an amount up to 0.5%, such up to 0.4%, such as up to 0.3%, such as up to 0.15%, such as in the range of 0.1% to 0.15%.

13. The method according to any one of claims 1-12, wherein said coating provides a functional layer on the surface of said fibre-containing composite material with a thickness of 10-30 nm.

14. Fibre reinforced composite material coated with an organo silane anchoring agent according to a method of claims 1-13.

15. A method for the production of an object made of a fibre reinforced composite material which methods comprises the sequential or simultaneous steps of

a) providing an organo silane anchoring agent; b) hydrolyzing said anchoring agent in an acidic aqueous solution having a pH lower than 3.2; c) coating a surface of said fibre reinforced composite material with the hydrolyzed anchoring agent; and d) then further coating the coated fibre reinforced composite material obtained under step c) with a paint, adhesive or other suitable surface coating.

16. The method according to claim 15, wherein at least two objects made of fibre reinforced composite material according to a method of claim 13 and further coated with an adhesive are bound together on the surface of the coatings.

17. The method according to any one of claims 15 or 16, wherein said object made of glass fibre reinforced composite material is a wind turbine blade.

18. Laminate or interconnected object of fibre reinforced composite material produced according to the method of claims 16-17.

19. Laminate or interconnected object according to claim 18, wherein the binding strength between laminate or interconnected objects is higher than 10 MPa, such as higher than 12, such as higher than 14 MPa, such as higher than 16 MPa, such as higher than 18 MPa, such as higher than 20 MPa, as measured by single lap shear tests using universal tensile test equipment.

20. Wind turbine blade made by a process according to claims 15-17, or made of a laminate or interconnected objects according to claim 18-19.

21. Wind turbine comprising one or more wind turbine blades according to claim 20.

22. A method for improving interfacial strength of a joint of two objects made of fibre reinforced composite material, said method comprising a step of providing at least one surface of said joint on one or both objects with at least one organo silane anchoring agent hydrolyzed in an acidic aqueous solution having a pH lower than 3.2.

23. A method for improving adhesion of a paint on a fibre reinforced composite material or other cover suitable for the covering said fibre reinforced composite material, said method comprising a step of

a) providing a surface of said fibre reinforced composite material with at least one organo silane anchoring agent hydrolyzed in an acidic aqueous solution having a pH lower than 3.2; and

b) applying said paint or other cover suitable for the covering said fibre reinforced composite material.