UV-curable wind turbine repair resin compositions

Abstract

The present invention provides a UV-curable wind turbine repair resin composition comprising an oligomer having a number average molecular weight of at least 1000, as measured by gel permeation chromatography according to the method provided in the methods section, one or more reactive diluent monomers, and a dual curing system comprising a free radical photoinitiator and a thermal initiator. The dual curing system is particularly suitable for improving the depth of cure to a UV-curable wind turbine repair resin composition and, when cured, maintains excellent mechanical and adhesion properties. The invention also relates to methods of curing and cured products made from the composition.

Description

[0001] UV-CURABLE WIND TURBINE REPAIR RESIN COMPOSITIONS

[0002] Field of the Invention

[0003] The present invention relates to a UV-curable wind turbine repair resin composition, methods of curing and cured products thereof.

[0004] Background

[0005] Wind turbines are becoming increasingly ubiquitous as environmentally safe and relatively inexpensive alternative energy sources. However, wind turbines are susceptible to both damage in the environment, such as from surface erosion, wear or lightning, and during and after in-factory manufacturing. In some cases, the damage sustained may be surface-level or cosmetic, which has an adverse effect on the efficiency and lifetime of the wind turbine. In more extreme cases, the damage sustained may be structural, which has an adverse effect on the operation, and so can increase the risk of a complete failure or breakdown of the wind turbine.

[0006] To maintain the upkeep of wind turbines so that they continue to be reliable and efficient, it is necessary to develop and optimise manufacturing and repair techniques. The repair may be post-production, infactory repair and in-field repair.

[0007] Conventional techniques for wind turbine blade repair involve a section-by-section repair approach, in which only a portion of the wind turbine to be repaired is cured at any given time. Typically, between each section and stage of the repair, the blade is only permitted to rotate at an angle between 30 to 45 degrees to avoid resin sagging and drippage. As a result, the repair of each section of the blade may in some cases require six hours, such as up to 8 hours, before the next section and stage of the repair is permitted to proceed.

[0008] Furthermore, conventional techniques also require a step of post-curing, which involves transferring the entire blade into an autoclave or oven at elevated temperatures, such as 80 °C or more. Naturally, such curing procedures requires a long thermal curing process, necessitating long man-hours for wind turbine repair processes. Moreover, high-temperature post-curing may also lead to undesirable strain in the materials due to different expansion coefficients in the respective fibre-reinforced composite materials composed in a wind turbine.

[0009] For these reasons, current methods used to repair wind turbines necessitate time, cost and human labour, including specialist repair methods and facilities. As such, the manufacture and repair of wind turbine parts is both complex and expensive.

[0010] It is known that UV curing may provide a route to a more efficient repair process due to the potentially faster curing. However, UV curing processes alone are limited to thin laminate curing because of the poor penetration of UV light required for a deeper cure. This poses a significant drawback in wind turbine repair as some parts of a wind turbine would otherwise require a light penetration of 70 mm for the deeper cure. Such repair processes employing a UV cure are described in the art.

[0011] For example, US 9970411 B2 discloses a UV-IR combination curing system and a method for manufacturing and repair composite parts, such as wind turbine manufacture and repair. The curing system employs a photoinitiator which is included in the layers of the composite material. The photoinitiator generates free radicals when exposed to UV radiation. However, the curing described in US 9970411 B2 requires a stagewise curing process to build up thickness of the cure.

[0012] WO 2023 / 012185 A1 discloses a composite material for wind turbine repair which uses a free-radical curing system comprising a peroxide. The peroxide is used to cure unsaturated functional groups in a polymerizable resin. However, WO 2023 / 012185 A1 requires a high curing temperature of over 70 °C.

[0013] In conclusion, conventional curing methods typically require significant amounts of time and energy to perform wind turbine repair, including practical implications as a result of the inherent size, complexity and magnitude of wind turbines.

[0014] Consequently, there remains a need within the art for improvements in the depth of cure of UV-curable wind turbine repair resin compositions in order to provide a faster and more cost-effective process, and without a high temperature input, for repairing wind turbine parts, in particular large parts of wind turbine, while also providing and maintaining good mechanical and structural performance for wind turbine applications.

[0015] The present invention has been devised in light of the above considerations.

[0016] Summary of the Invention

[0017] In a first aspect of the invention, there is provided a UV-curable wind turbine repair resin composition comprising:

[0018] (a) an oligomer having a number average molecular weight Mn of at least 1000, as measured by gel permeation chromatography according to the method provided in the methods section,

[0019] (b) one or more reactive diluent monomers; and

[0020] (c) a dual curing system comprising:

[0021] (i) a free radical photoinitiator for initiating a free radical polymerisation reaction in the UV- curable wind turbine repair resin composition; and

[0022] (ii) a thermal initiator for initiating a further free radical polymerisation reaction in the UV- curable wind turbine repair resin composition, wherein the thermal initiator is heat-activatable from the initiation of a free radical polymerisation by the free radical photoinitiator.

[0023] Surprisingly, the inventors have found that, once cured, UV-curable wind turbine repair resin compositions of the first aspect, which employ a dual curing system having the combination of a free radical photoinitiator and a thermal initiator, achieves a significantly deeper cure while maintaining a combination of mechanical properties. Hence, the need for a post-cure step as described in the art is entirely eliminated, and the requirements of time and energy necessary for performing the repair procedures are significantly reduced. In addition to the improved cure, making it useful for providing a route to a more rapid repair of a wind turbine part, the cured product also has good mechanical properties, such as tensile modulus, peak tensile stress, peak tensile strain, flexural modulus, peak flexural stress and peak flexural strain, and good adhesion properties, such as z-direction tensile stress at maximum load.

[0024] Without wishing to be bound by theory, it is believed that the improved cure is achieved by the dual curing system having the combination of a free radical photoinitiator and a thermal initiator. Suitably, the UV- curable wind turbine repair resin composition of the first aspect can undergo a curing process in which polymerisation takes place when exposed to the free radical photoinitiator and the thermal initiator.

[0025] Firstly, the free radical photoinitiator can initiate the curing process when exposed to UV radiation. An elevated temperature is generated by the free radical photoinitiator as it initiates the curing process because the free radical polymerisation is an exothermic reaction. Therefore, the heat is generated within the UV-curable wind turbine repair resin composition. Secondly, the thermal initiator can then propagate the curing process when exposed to this elevated temperature generated from the initial UV-induced cure.

[0026] Therefore, the inventors have found that the dual curing system of the first aspect is capable of curing at a depth at which there is no penetration of UV light. This means that the UV-induced curing via the dual curing system is capable of curing at a deeper depth compared to conventional UV-induced curing, despite both curing processes being initiated by UV light and thus having the same limitation in UV light penetration.

[0027] It is also believed that an oligomer having a number average molecular weight Mn of at least 1000, as measured by gel permeation chromatography according to the method provided in the methods section, provides the cured product with good mechanical properties owing to the relatively high molecular weight of the oligomeric chain. In some embodiments, the oligomer has a number average molecular weight Mn of at least 2000, as measured by gel permeation chromatography according to the method provided in the methods section.

[0028] In some embodiments, the oligomer is a vinyl ester oligomer. In some embodiments, the oligomer is a vinyl ester oligomer derived from:

[0029] (i) an epoxy compound comprising at least two epoxy groups;

[0030] (ii) an aromatic chain-extending reagent comprising at least two hydroxyl groups or at least two carboxylic acid groups; and

[0031] (iii) a compound selected from an a,p-unsaturated monocarboxylic acid, a (meth)acrylate ester or a (meth)acrylate anhydride, such as methacrylic acid. In the first aspect of the invention, the UV-curable wind turbine repair resin composition comprises a thermal initiator - that is to say, the thermal initiator is contained in the composition.

[0032] In another aspect of the invention, the UV-curable wind turbine repair resin composition comprises the free radical photoinitiator and is supplied together with a thermal initiator in a kit - that is to say, the thermal initiator is not pre-added to the UV-curable wind turbine repair resin composition or the UV- curable wind turbine repair resin composition. The two components of the dual curing system are therefore separated before they are then combined to produce the UV-curable wind turbine repair resin composition of the first aspect.

[0033] Thus, suitably, in a second aspect of the invention, there is provided is a wind turbine repair kit comprising:

[0034] (1) a UV-curable wind turbine repair resin composition comprising:

[0035] (a) an oligomer having a number average molecular weight Mn of at least 1000, as measured by gel permeation chromatography according to the method provided in the methods section,

[0036] (b) one or more reactive diluent monomers; and

[0037] (c) a free radical photoinitiator for initiating a free radical polymerisation reaction in the UV- curable wind turbine repair resin composition; and

[0038] (2) a thermal initiator for initiating a further free radical polymerisation reaction in the UV-curable wind turbine repair resin composition, wherein the thermal initiator is heat-activatable from the initiation of a free radical polymerisation by the free radical photoinitiator.

[0039] When the UV-curable wind turbine repair resin composition does not comprise the thermal initiator, it is herein referred to as the UV-curable wind turbine repair resin composition of the second aspect.

[0040] A third aspect of the invention is the use of the dual curing system of the first aspect or the kit of the second aspect for improving the depth of cure to a UV-curable wind turbine repair resin composition via free radical polymerisation. By providing the use of a dual curing system of the first aspect or the kit of the second aspect, the need for a post-cure step as described in the art is entirely eliminated, and the requirements of time and energy necessary for performing the repair procedures are significantly reduced.

[0041] A fourth aspect of the invention is a method of curing the UV-curable wind turbine repair resin composition of the first aspect or the second aspect, the method comprising the steps of:

[0042] (i) exposing the UV-curable wind turbine repair resin composition and a free radical photoinitiator to UV light to initiate a cure via a free radical polymerisation, and generating heat in the UV-curable wind turbine repair resin composition; and

[0043] (ii) exposing the UV-curable wind turbine repair resin composition and a thermal initiator to the heat generated in step (i) to initiate a further cure in the UV-curable wind turbine repair resin composition via the free radical polymerisation. A fifth aspect of the invention is a cured product of the UV-curable wind turbine repair resin composition obtained from the method of the fourth aspect.

[0044] A sixth of the invention is a wind turbine part comprising the cured product of the fifth aspect.

[0045] The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

[0046] Preferred embodiments of the invention may also include any one or more of the following preferred features. Preferred features mentioned in relation to the first aspect of the invention may apply equally to the other aspects.

[0047] Summary of the Figures

[0048] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0049] Figure 1 shows the degree of cure of glass laminates having a total thickness of 40 layers at various depths of the material (10 layers, 20 layers and 30 layers) as a function of temperature over the curing time. Each glass layer has a thickness of around 1 mm.

[0050] Detailed Description of the Invention

[0051] As used herein, the term “(meth)acrylate” refers to both or any one of “acrylate” and “methacrylate” and this well-known abbreviation will be used throughout.

[0052] As used herein, the term “chain-extending reagent” refers to a compound which, when incorporated into the vinyl ester oligomer by reaction, increases the length and molecular weight of the molecular chain.

[0053] As used herein, the term “monomer” refers to a small molecule that may chemically react and become chemically bonded with itself or with other monomers to form a polymer.

[0054] As is well understood in the field of polymer chemistry, an oligomer is a low molecular weight polymer obtained by reaction of molecules having lower molecular weights. The oligomer may in some instances contain a small number of repeating sequences of the lower molecular weight molecules, for example two repeating sequences, three repeating sequences or four repeating sequences. The oligomer may in some instances contain five or more repeating sequences.

[0055] As is well understood by those skilled in the art, the preparation of products of this nature inevitably results in a mixture of molecular structures with differing molecular weights, depending on the degree of polymerisation and the extent of incorporation of each monomer. The oligomer component of the UV-curable wind turbine repair resin composition of the invention has a number average molecular weight Mn of at least 1000, as measured by gel permeation chromatography according to the method provided in the methods section.

[0056] In some embodiments, the oligomer has a number average molecular weight Mn of at least 1100, such as at least 1100, such as at least 1200, such as at least 1300, such as at least 1400, such as at least 1500, such as at least 1600, such as at least 1700, such as at least 1800, such as at least 1900, such as at least 2000, as measured by gel permeation chromatography according to the method provided in the methods section.

[0057] In some embodiments, the oligomer has a number average molecular weight Mn of at most 5000, such as at most 4500, such as at most 4000, such as at most 3500, such as at most 3000, as measured by gel permeation chromatography according to the method provided in the methods section.

[0058] Examples of suitable oligomers for wind turbine repair resin compositions typically have a number average molecular weight Mn of between 1000 to 5000, such as between 1200 to 5000, such as between 1400 to 4500, such as between 1500 to 4500, such as between 2000 to 4500, such as between 2000 to 4000, such as between 2000 to 3500, such as between 2000 to 3000, as measured by gel permeation chromatography according to the method provided in the methods section.

[0059] In some embodiments, the oligomer is present, based on the total weight of the wind turbine repair resin composition, in an amount of at least 20 wt%, such as at least 25 wt%, such as at least 30 wt%, such as at least 35 wt%, such as at least 40 wt%.

[0060] In some embodiments, the oligomer is present, based on the total weight of the wind turbine repair resin composition, in an amount of at most 70 wt%, such as at most 65 wt%, such as at most 60 wt%, such as at most 55 wt%, such as at most 50 wt%.

[0061] In some embodiments, the oligomer is present, based on the total weight of the wind turbine repair resin composition, in an amount from 20 to 70 wt%, such as from 25 to 65 wt%, such as from 30 to 60 wt%, such as from 35 to 55 wt%, such as from 40 to 50 wt%.

[0062] Preferably, the oligomer is a vinyl ester oligomer. As used herein, the term “vinyl ester oligomer” refers to an oligomer obtained from the esterification of an epoxy resin with (meth)acrylates and their derivatives.

[0063] In some embodiments, the vinyl ester oligomer is derived from, or is the reaction product of:

[0064] (i) an epoxy compound comprising at least two epoxy groups;

[0065] (ii) a chain-extending reagent; and

[0066] (iii) a compound selected from an a,p-unsaturated monocarboxylic acid, a (meth)acrylate ester or a (meth)acrylate anhydride.

[0067] In some embodiments, the epoxy group of the epoxy compound is capable of reacting with a suitable functional group of the chain-extending reagent, such as a hydroxyl group or a carboxylic acid group, via an epoxide ring-opening reaction. In some embodiments, the epoxy group is bisphenol A diglycidyl ether.

[0068] In some embodiments, the chain-extending reagent is an aromatic chain-extending reagent.

[0069] In some embodiments, the chain-extending reagent comprises at least two hydroxyl groups or at least two carboxylic acid groups.

[0070] In some embodiments, the chain-extending reagent is bisphenol A.

[0071] In some embodiments, the a,p-unsaturated monocarboxylic acid is methacrylic acid.

[0072] In some embodiments, the (meth)acrylate ester is a methacrylate ester, such as glycidyl methacrylate.

[0073] In some embodiments, the (meth)acrylate anhydride is a methacrylic anhydride.

[0074] Thus, for example the vinyl ester oligomer may be prepared by reacting two moles of an epoxy compound, such as bisphenol A diglycidyl ether, with one mole of a chain-extending reagent, such as bisphenol A, to form a vinyl ester pre-polymer. The resulting vinyl ester pre-polymer could then be reacted with two moles of a compound which acts as an end-capping reagent, such as methacrylic acid, to give a vinyl ester oligomer, which would have a theoretical structure A-(X-Y-X)n-A, in which A is the end-capping reagent, X is the epoxy compound, Y is the chain-extending reagent and n is an integer representing the number of X-Y-X sequences. For example, n is selected from 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10 or more.

[0075] As is well understood by those skilled in the art, the preparation of products of this nature inevitably results in a mixture of molecular structures with differing molecular weights, having a variety of values of n. The relative proportions of epoxy compound (X) and chain-extending reagent (Y) determines the average value of n for what is in practice, a mixture of similar vinyl ester oligomer structures.

[0076] In some embodiments, the vinyl ester oligomer is present, based on the total weight of the vinyl ester resin composition, in an amount of at least 20 wt%, such as at least 25 wt%, such as at least 30 wt%, such as at least 35 wt%, such as at least 40 wt%.

[0077] In some embodiments, the vinyl ester oligomer is present, based on the total weight of the vinyl ester resin composition, in an amount of at most 70 wt%, such as at most 65 wt%, such as at most 60 wt%, such as at most 55 wt%, such as at most 50 wt%.

[0078] In some embodiments, the vinyl ester oligomer is present, based on the total weight of the vinyl ester resin composition, in an amount from 20 to 70 wt%, such as from 25 to 65 wt%, such as from 30 to 60 wt%, such as from 35 to 55 wt%, such as from 40 to 50 wt%.

[0079] In some embodiments, the UV-curable filler composition further comprises a vinyl ester trimer. In some embodiments, the vinyl ester trimer is a trimer derived from, or is the reaction product of: (i) an epoxy compound comprising at least two epoxy groups, (ii) a chain-extending reagent, and (iii) a compound selected from an a,p-unsaturated monocarboxylic acid, a (meth)acrylate ester or a (meth)acrylate anhydride. That is, the vinyl ester trimer comprises less than two units of each of (i) to (iii). In some embodiments, the vinyl ester trimer has a molecular weight of at least 500, as measured by gel permeation chromatography according to the method provided in the methods section.

[0080] Reactive diluent monomer

[0081] A reactive diluent monomer of the UV-curable wind turbine repair composition may be any reactive diluent monomer known in the art. The term “reactive monomer diluent” refers to any reactive monomer which is capable of reducing the viscosity of a resin, the reactive monomer being in liquid form at room temperature and being curable with the vinyl ester oligomer.

[0082] The reactive diluent monomer may be selected from a monofunctional reactive diluent monomer or a polyfunctional reactive diluent monomer, or a combination thereof. The polyfunctional reactive diluent may be selected from a difunctional reactive diluent monomer, a trifunctional reactive diluent monomer or a tetrafunctional reactive diluent monomer, or a combination thereof.

[0083] Suitable examples of monofunctional reactive diluent monomers include hydroxyl ethyl (meth)acrylate, hydroxyl propyl (meth)acrylate, butyl (meth)acrylate, vinyl toluene, hexyl (meth)acrylate and cyclohexyl (meth)acrylate, a-methyl styrene, t-butyl styrene, phenoxyethyl (meth)acrylate, tetrahydro furfuryl, (meth)acrylate, allyl (meth)acrylate, tetrahydro furfuryl (meth)acrylate, hydroxyl ethyl (meth)acrylate, hydroxyl propyl (meth)acrylate and benzyl methacrylate.

[0084] Suitable examples of difunctional reactive diluent monomers include PEG200 di(meth)acrylate, 1 ,4- butanediol di(meth)acrylate, 1 ,3-butanediol di(meth)acrylate, 2,3-butanedioldi(meth)acrylate, 1 ,6- hexanediol di(meth)acrylate and its isomers, diethyleneglycol di(meth)acrylate, triethyleneglycol di(meth)acrylate, glycerol di(meth)acrylate, trimethylolpropane di(meth)acrylate, neopentyl glycol di(meth)acrylate, dipropyleneglycol di(meth)acrylate, tripropyleneglycol di(meth)acrylate, PPG250 di(meth)acrylate, tricyclodecane dimethylol di(meth)acrylate, 1 ,10-decanediol di(meth)acrylate and / or tetraethylene glycol dimethacrylate.

[0085] Suitable trifunctional reactive diluent monomers include trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, propoxylated glycerine tri(meth)acrylate, pentaerythritol tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, and tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate.

[0086] Suitable tetrafunctional reactive diluent monomers include pentaerythritol tetra(meth)acrylate, ethoxy modified products of pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, ethoxy modified products of ditrimethylolpropane tetra(meth)acrylate, and condensation reaction products of trimethylolethane, acrylic acid and succinic anhydride.

[0087] The reactive diluent monomer may also be a vinyl aromatic, such as a styrene monomer or a styrene derivative monomer. Suitable styrene derivative monomers, if used, include alpha-methyl styrene, vinyl toluene, ethyl styrene, 2-chlorostyrene, 3-chlorostyrene, 4-chlorostyrene, 2-bromostyrene, 3- bromostyrene, 4-bromostyrene, alpha-bromostyrene, beta-bromostyrene and tert-butyl styrene. The composition and characteristics of the UV-curable wind turbine repair resin composition may be modified by adjusting the relative amount of each reactive diluent monomer.

[0088] Suitably, the UV-curable wind turbine repair resin composition, such as a vinyl ester resin composition, comprises a reactive diluent monomer mixture comprising one or more reactive diluent monomers, such as two or more reactive diluent monomers, such as three or more reactive diluent monomers.

[0089] In some embodiments, the reactive diluent monomer mixture comprises a monofunctional methacrylate and a polyfunctional acrylate.

[0090] In some embodiments, the reactive diluent monomer mixture comprises a monofunctional methacrylate and a difunctional acrylate or a trifunctional acrylate. In some embodiments, the reactive diluent monomer mixture comprises a monofunctional methacrylate, a difunctional acrylate and a trifunctional acrylate.

[0091] In some preferred embodiments, the styrene monomer is present in an amount, based on the total weight of the UV-curable wind turbine repair resin composition, in an amount of less than 5 wt% of styrene monomer, preferably less than 3 wt% of styrene monomer, more preferably less than 1 wt% of styrene monomer.

[0092] In some preferred embodiments, the UV-curable wind turbine repair resin composition is substantially free of styrene. As used herein, the term “substantially free of styrene” means that the UV-curable wind turbine repair resin compositions are formulated without the inclusion of any styrene monomer. For example, the UV-curable wind turbine repair resin composition comprises less than 0.05 wt% of styrene monomer, preferably less than 0.03 wt% of styrene monomer, more preferably less than 0.01 wt% of styrene monomer.

[0093] In some embodiments, the reactive diluent monomer is present, based on the total weight of the vinyl ester resin composition, in an amount of at least 25%, such as at least 30 wt%, such as at least 35 wt%, such as at least 37 wt%, such as at least 39 wt%, such as at least 41 wt%, such as at least 43 wt%, such as at least 45 wt%, such as at least 47 wt%, such as at least 49 wt%, such as at least 51 wt%.

[0094] In some embodiments, the reactive diluent monomer is present, based on the total weight of the vinyl ester resin composition, in an amount of at most 80 wt%, such as at most 75 wt%, such as at most 70 wt%, such as at most 69 wt%, such as at most 67 wt%, such as at most 65 wt%, such as at most 63 wt%, such as at most 61 wt%, such as at most 59 wt%, such as at most 57 wt%, such as at most 55 wt%, such as at most 53 wt% .

[0095] In some embodiments, the reactive diluent monomer is present, based on the total weight of the vinyl ester resin composition, in an amount from 25 wt% to 80 wt%, such as 30 wt% to 75 wt%, such as 35 wt% to 70 wt%, such as 35 wt% to 69 wt%, such as 37 wt% to 67 wt%, such as 39 wt% to 65 wt%, such as 41 wt% to 63 wt%, such as 43 wt% to 61 wt %, such as 45 wt% to 59 wt%, such as 47 wt % to 57 wt%, such as 49 wt% to 55 wt%, such as 51 wt% to 53 wt%. Free radical

[0096] Photoinitiators tend to initiate, enable, facilitate or catalyse chemicals reactions that result in or improve the rate or amount of polymerisation in a given composition when it is subjected to appropriate amounts of actinic radiation. A photoinitiator is a compound that undergoes a photoreaction upon absorption of actinic radiation (particularly in the visible and / or UV spectral region), whereupon reactive species are created. These reactive species are capable of catalysing, initialising or carrying out chemical reactions that result in significant changes in the physical properties of suitable formulations. Hence, the photoinitiator is a compound that can transform the physical energy of light into suitable chemical energy in the form of reactive intermediates. Common types of photoinitiators include cationic photoinitiators and free-radical photoinitiators.

[0097] The dual curing system for the UV-curable wind turbine repair resin composition comprises a free radical photoinitiator as a first component, and is combined with a thermal initiator as a second component. When exposed to actinic radiation, a free radical photoinitiator creates free radicals as the reactive species.

[0098] The free radical photoinitiator is for initiating a free radical polymerisation reaction in the UV-curable wind turbine repair resin composition.

[0099] In some embodiments, the free-radical photoinitiator is selected from a phosphine oxide (such as a benzoyl phosphine oxide), an aryl ketone, a benzophenone, a hydroxylated ketone, a ketal, a metallocene, or a combination thereof.

[0100] In some embodiments, the free-radical photoinitiator is selected from 2,4,6-trimethylbenzoyl diphenylphosphine oxide, ethyl(2,4,6-trimethylbenzoyl)-phenyl phosphinate, bis(2,4,6-trimethylbenzoyl)- phenylphosphine oxide, diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide, 2-methyl-1-[4- (methylthio)phenyl]-2-morpholinopropanone-1 ,2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1- butanone, 2-dimethylamino-2-(4-methyl-benzyl)-1 -(4-morpholin-4-yl-phenyl)-butan-1 -one, 4-benzoyl-4'- methyl diphenyl sulphide, 4,4'-bis(diethylamino) benzophenone, 4,4'-bis(N,N'-dimethylamino) benzophenone [Michler's ketone], benzophenone, 4-methyl benzophenone, 2,4,6-trimethyl benzophenone, dimethoxybenzophenone, acetophenone, chlorinated acetophenone, dialkoxyacetophenones, dialkylhydroxyacetophenones, dialkylhydroxyacetophenone esters, benzoin acetate, benzoin, benzoin alkyl ethers, dimethoxybenzoin, dibenzylketone, 1 -hydroxycyclohexyl phenyl ketone, phenyl (l-hydroxyisopropyl)ketone, 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1- propanone, 4-isopropylphenyl(1-hydroxyisopropyl)ketone, oligo-[2-hydroxy-2-methyl-1-[4-(1 - methylvinyl)phenyl] propanone], camphorquinone, 4,4'-bis(diethylamino) benzophenone, benzil dimethyl ketal, bis(eta 5-2-4-cyclopentadien-1-yl)bis[2,6-difluoro-3-(1 H-pyrrol-1-yl)phenyl]titanium, benzoylcyclohexanol, acyloxime esters, acylphosphine oxides, acylphosphonates, ketosulfides, dibenzoyldisulfides, diphenyl dithiocarbonate, and any combination thereof.

[0101] Further free-radical photoinitiators include: benzoylphosphine oxides, such as, for example, 2,4,6- trimethylbenzoyl diphenylphosphine oxide (Lucirin TPO from BASF) and 2,4,6-trimethylbenzoyl phenyl, ethoxy phosphine oxide (Lucirin TPO-L from BASF), bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide (Irgacure 819 or BAPO from BASF), 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone-1 (Irgacure 907 from IGM Resins), 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl) phenyl]-1-butanone (Irgacure 369 from IGM Resins), 2-dimethylamino-2-(4-methyl-benzyl)-1-(4-morpholin-4-yl-phenyl)-butan- 1-one (Irgacure 379 from IGM Resins), 4-benzoyl-4'-methyl diphenyl sulphide (Chivacure BMS from

[0102] Chitec), 4,4'-bis(diethylamino) benzophenone (Chivacure EMK from Chitec), 4,4'-bis(N,N'-dimethylamino) benzophenone (Michler's ketone), camphorquinone, and metallocenes such as bis(eta 5-2-4- cyclopentadien-1-yl)bis[2,6-difluoro-3-(1 H-pyrrol-1-yl)phenyl] titanium (Irgacure 784 from IGM Resins), or a mixture thereof.

[0103] In some embodiments, the free-radical photoinitiator is a phosphine oxide. In some embodiments, where a plurality of free radical photoinitiators are used, the free radical photoinitiators comprise a phosphine oxide.

[0104] In some embodiments, the free radical photoinitiator is present, based on the total weight of the UV- curable wind turbine repair resin composition, in an amount of at least 0.01 wt%, such as at least 0.1 wt%, such as at least 0.2 wt%, such as at least 0.3 wt%, such as at least 0.4 wt%, such as at least 0.5 wt%.

[0105] In some embodiments, the free radical photoinitiator is present, based on the total weight of the UV- curable wind turbine repair resin composition, in an amount of at most 10 wt%, such as at most 8 wt%, such as at most 6 wt%, such as at most 4 wt%, such as at most 2 wt%, such as at most 1 .5 wt%.

[0106] In some embodiments, the free radical photoinitiator is present, based on the total weight of the UV- curable wind turbine repair resin composition, in an amount from 10 wt% to 0.01 wt%, such as 0.5 wt% to 1 .5 wt%.

[0107] Suitably, the free radical photoinitiator may be pre-added into the UV-curable wind turbine repair resin composition. The thermal initiator is then not pre-added to the UV-curable wind turbine repair resin composition.

[0108] In some embodiments, the free radical photoinitiator is present, based on the total weight of the UV- curable wind turbine repair resin composition, in an amount of at least 0.01 wt%, such as at least 0.1 wt%, such as at least 0.2 wt%, such as at least 0.3 wt%, such as at least 0.4 wt%, such as at least 0.5 wt%.

[0109] In some embodiments, the free radical photoinitiator is present, based on the total weight of the UV- curable wind turbine repair resin composition, in an amount of at most 10 wt%, such as at most 8 wt%, such as at most 6 wt%, such as at most 4 wt%, such as at most 2 wt%, such as at most 1 .5 wt%.

[0110] In some embodiments, the free radical photoinitiator is present, based on the total weight of the UV- curable wind turbine repair resin composition, in an amount from 10 wt% to 0.01 wt%, such as 0.5 wt% to 1 .5 wt%. In some embodiments, the free radical photoinitiator is present, based on the total weight of the dual curing system, in an amount at least 20 wt% such as at least 30 wt%, such as at least 40 wt%, such as at least 50 wt%, such as at least 60 wt%, such as at least 70 wt%, such as at least 80 wt%.

[0111] In some embodiments, the free radical photoinitiator is present, based on the total weight of the dual curing system, in an amount at most 80 wt% such as at most 70 wt%, such as at most 60 wt%, such as at most 50 wt%, such as at most 40 wt%, such as at most 30 wt%, such as at most 20 wt%.

[0112] In some embodiments, the free radical photoinitiator is present, based on the total weight of the dual curing system, in an amount from 20 wt% to 80 wt%, 30 wt% to 70 wt%, such as 40 wt% to 60 wt%.

[0113] Thermal initiator

[0114] Thermal initiators tend to initiate, enable, facilitate or catalyse chemicals reactions that result in or improve the rate or amount of polymerisation in a given composition when it is subjected to appropriate temperatures. A thermal initiator is a compound that undergoes decomposition at specific temperatures, whereupon reactive species are created. These reactive species are capable of catalysing, initialising or carrying out chemical reactions that result in significant changes in the physical properties of suitable formulations. Hence, the thermal initiator is a compound that can yield an appreciable amount of reactive intermediates at elevated temperatures. Common types of thermal initiators include peroxide thermal initiators and azo compound thermal initiators.

[0115] The dual curing system for the UV-curable wind turbine repair resin composition comprises a thermal initiator as a first component, and is combined with a free radical photoinitiator as a second component.

[0116] The thermal initiator is for initiating a further free radical polymerisation reaction in the UV-curable wind turbine repair resin composition, wherein the thermal initiator is heat-activable from the initiation of a free radical polymerisation by the free radical photoinitiator.

[0117] Therefore, the thermal initiator of the dual curing system is activated by heat, such as heat generated from the initiation using the free radical photoinitiator of the dual curing system. In other words, the thermal initiator is heat-activatable. The heat generated is sufficient to raise the temperature of at least a portion of the UV-curable wind turbine repair resin composition above the 1-hour half-life temperature, the 10-hour half-life temperature or the self-accelerating decomposition temperature of the thermal initiator.

[0118] An important indicator of activity of a thermal initiator is its half-life (tic). It is the time required to reduce the original thermal initiator content of a solution by 50% at a given temperature. The activity may also depend on the solvent system used.

[0119] Most commonly, the decomposition rate of a thermal initiator may be characterised by its 1-hour half-life (tie) temperature or its 10-half half-life (tic) temperature in a particular solvent. That is, the 1-hour halflife temperature is the temperature at which an original thermal initiator content of a solution is reduced by 50% after 1 hour. The 10-hour half-life temperature is the temperature at which an original thermal initiator content of a solution is reduced by 50% after 10 hours. In some embodiments, the thermal initiator has a 1-hour half-life temperature of 120 °C or less, such as a 1-hour half-life temperature of 110 °C or less, such as a 1-hour half-life temperature of 100 °C or less, such as a 1 -hour half-life temperature of 95 °C or less, such as a 1 -hour half-life temperature of 90 °C or less, such as a 1 -hour half-life temperature of 85 °C or less, such as a 1 -hour half-life temperature of 80 °C or less, such as a 1-hour half-life temperature of 75 °C or less, such as a 1-hour half-life temperature of 70 °C or less, such as a 1-hour half-life temperature of 65 °C or less, such as a 1-hour half-life temperature of 60 °C or less, such as a 1-hour half-life temperature of 55 °C or less, such as a 1-hour half-life temperature of 50 °C or less, such as a 1-hour half-life temperature of 45 °C or less, such as a 1- hour half-life temperature of 40 °C or less, wherein the 1-hour half-life temperature is measured in chlorobenzene.

[0120] In some embodiments, the thermal initiator has a 10-hour half-life temperature of 100 °C or less, such as a 10-hour half-life temperature of 95 °C or less, such as a 10-hour half-life temperature of 90 °C or less, such as a 10-hour half-life temperature of 85 °C or less, such as a 10-hour half-life temperature of 80 °C or less, such as a 10-hour half-life temperature of 75 °C or less, such as a 10-hour half-life temperature of 70 °C or less, such as a 10-hour half-life temperature of 65 °C or less, such as a 10-hour half-life temperature of 60 °C or less, such as a 10-hour half-life temperature of 55 °C or less, such as a 10-hour half-life temperature of 50 °C or less, such as a 10-hour half-life temperature of 45 °C or less, such as a 10-hour half-life temperature of 40 °C or less, wherein the 10-hour half-life temperature is measured in chlorobenzene.

[0121] In some embodiments, the thermal initiator has a 1-hour half-life temperature of 95 °C or less as measured in chlorobenzene.

[0122] In some embodiments, the thermal initiator has a 10-hour half-life temperature of 75 °C or less as measured in chlorobenzene.

[0123] Another indicator of activity of a thermal initiator is its self-accelerating decomposition temperature (SADT). The self-accelerating decomposition temperature (SADT) of a thermal initiator is the lowest ambient temperature at which the thermal initiator in a typical vessel or package will undero a selfaccelerating decomposition within one week. The self-accelerating decomposition temperature (SADT) is in accordance with the Heat Accumulation Storage Test (HAST).

[0124] In some embodiments, the thermal initiator has a self-accelerating decomposition temperature of 100 °C or less, such as 95 °C or less, such as 90 °C or less, such as 85 °C or less, such as 80 °C or less, such as 75 °C or less, such as 70 °C or less, such as 65 °C or less, such as 60 °C or less, such as 55 °C or less, such as 50 °C or less, such as 45 °C or less, such as 40 °C or less, such as 35 °C or less, such as 30 °C or less, such as 25 °C or less, wherein the self-accelerating decomposition temperature is measured in accordance with the Heat Accumulation Storage Test (HAST).

[0125] In some embodiments, the thermal initiator has a self-accelerating decomposition temperature of 40 °C or less as measured in accordance with the Heat Accumulation Storage Test (HAST). In some embodiments, the thermal initiator initiates a free radical polymerisation in response to an elevated temperature at a temperature of at least 25 °C, such as at least 30 °C, such as at least 40 °C, such as at least 50 °C, such as at least 60 °C. In some embodiments, the thermal initiator initiates a free radical polymerisation in response to an elevated temperature at a temperature of from 25 to 200 °C, such as from 30 to 150 °C, such as from 40 to 120 °C, such as from 50 to 90 °C, such as from 60 to 80 °C.

[0126] In some embodiments, the thermal initiator is an organic thermal peroxide. In some embodiments, the thermal initiator is a thermal perester peroxide.

[0127] In some embodiments, the organic thermal peroxide comprises a hydroxyl terminus. In some embodiments, the organic thermal peroxide comprises an alkyl or acyl terminus.

[0128] Suitably, the thermal initiator may be selected from tert-amyl peroxybenzoate, 4,4-azobis(4-cyanovaleric acid), 1 ,1'-azobis(cyclohexanecarbonitrile), 2,2'-azobisisobutyronitrile (AIBN), benzoyl peroxide, 2,2- bis(tert-butylperoxy)butane, 1 ,1-bis(tert-butylperoxy)cyclohexane, 2,5-bis(tert-butylperoxy)-2,5- dimethylhexane, 2,5-bis(tert-butylperoxy)-2,5-dimethy l-3-hexyne, bis (1 -(tert-butylperoxy)-l - methylethyl)benzene, 1 ,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, tert-butyl hydroperoxide, tert-butyl peracetate, tert-butyl peroxide, tert-butyl peroxybenzoate, tert-butylperoxy isopropyl carbonate, cumene hydroperoxide, cyclohexanone peroxide, dicumyl peroxide, lauroyl peroxide, 2,4-pentanedione peroxide, peracetic acid, potassium persulfate, and any combination thereof.

[0129] Further thermal initiators include, for example, Diisobutyryl peroxide (TRIGONOX 187 from Nouryon), Cumyl peroxyneodecanoate (TRIGNOX 99 from Nouryon), 1 ,1 ,3,3-Tetramethylbutyl peroxyneodecanoate (TRIGONOX 423 from Nouryon), tert-Amyl peroxyneodecanoate (TRIGONOX 123 from Nouryon), Di-sec- butyl peroxydicarbonate (TRIGONOX SBP from Nouryon), Di(4-tert-butylcyclohexyl) peroxydicarbonate (PERKADOX 16 from Nouryon), Di(2-ethylhexyl) peroxydicarbonate (TRIGONOX EHP from Nouryon), tert-Buty I peroxyneodecanoate (TRIGONOX 23 from Nouryon), Dicetyl peroxydicarbonate (PERKADOX 24 from Nouryon), Dimyristyl peroxydicarbonate (PERKADOX 26 from Nouryon), 1 ,1 ,3,3-Tetramethylbutyl peroxypivalate (TRIGONOX 425 from Nouryon), tert-Amyl peroxypivalate (TRIGONOX 125 from Nouryon), tert-Butyl peroxypivalate (TRIGONOX 25 from Nouryon), Di(3,5,5-trimethylhexanoyl) peroxide (TRIGONOX 36 from Nouryon), Dilauroyl peroxide (LAUROX from Nouryon), 2,5-Dimethyl-2,5-di(2- ethylhexanoylperoxy)hexane (TRIGONOX 141 from Nouryon), Di(4-methylbenzoyl) peroxide (PERKADOX PM-W75 from Nouryon), 1 ,1 ,3,3-Tetramethylbutyl peroxy-2-ethylhexanoate (TRIGONOX 421 from Nouryon), tert-Amyl peroxy-2-ethylhexanoate (TRIGONOX 121 from Nouryon), Dibenzoyl peroxide (PERKADOX L from Nouryon), tert-Butyl peroxy-2-ethylhexanoate (TRIGONOX 21 S from Nouryon), tert-Butyl peroxyisobutyrate (TRIGONOX 41 from Nouryon), 1 ,1-Di(tert- amylperoxy)cyclohexane (TRIGONOX 122 from Nouryon), 1 ,1-Di(tert-butylperoxy)-3,3,5- trimethylcyclohexane (TRIGONOX 29 from Nouryon), 1 ,1-Di(tert-butylperoxy)cyclohexane (TRIGONOX 22 from Nouryon), tert-Amyl peroxy 2-ethylhexyl carbonate (TRIGONOX 131 from Nouryon), tert-Butyl peroxy-3,5,5-trimethylhexanoate (TRIGONOX 42 from Nouryon), 2,2-Di(tert-butylperoxy)butane (TRIGONOX D-C50* from Nouryon), tert-Butylperoxy isopropyl carbonate (TRIGONOX BPIC-C75* from Nouryon),), tert-Amyl peroxybenzoate (TRIGONOX 127 from Nouryon), tert-Butyl peroxyacetate (TRIGONOX F-C50 from Nouryon), tert-Butyl peroxybenzoate (TRIGONOX C from Nouryon), Dicumyl peroxide (PERKADOX BC-FF from Nouryon), Di(tert-butylperoxyisopropyl)benzene (PERKADOX 14S from Nouryon), 2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane (TRIGONOX 101 from Nouryon), Di-tert-butyl peroxide (TRIGONOX B from Nouryon), 3,6,9-Triethyl-3,6,9-trimethyl-1 ,4,7-triperoxonane (TRIGONOX 301 from Nouryon), 1 ,2,4,5,7,8-Hexoxonane, 3,6,9-trimethyl-3,6,9-tris (Et and Pr) (TRIGONOX 501 from Nouryon), 1 ,1 ,3,3-Tetramethylbutyl hydoperoxide (TRIGONOX TMBH-L from Nouryon), Cumyl hydroperoxide (TRIGONOX K from Nouryon), tert-Butyl hydroperoxide (TRIGONOX A from Nouryon), tert-Amyl hydroperoxide (TRIGONOX TAHP-W85 from Nouryon), and azo compounds, such as, for example, 2,2’-Azodi(isobutyronitrile) (PERKADOX AIBN from Nouryon), 2,2’-Azodi(2-methylbutyronitrile) (PERKADOX AMBN from Nouryon), 1 ,1 ’-Azodi(hexahydrobenzonitrile) (PERKADOX ACCN from Nouryon), or a mixture thereof.

[0130] In some embodiments, the thermal initiator is present, based on the total weight of the wind turbine repair resin composition, in an amount of at least 0.01 wt%, such as at least 0.1 wt%, such as at least 0.2 wt%, such as at least 0.3 wt%, such as at least 0.4 wt%, such as at least 0.5 wt%.

[0131] In some embodiments, the thermal initiator is present, based on the total weight of the wind turbine repair resin composition, in an amount of at most 10 wt%, such as at most 8 wt%, such as at most 6 wt%, such as at most 4 wt%, such as at most 2 wt%, such as at most 1 .5 wt%.

[0132] In some embodiments, the thermal initiator is present, based on the total weight of the wind turbine repair resin composition, in an amount from 10 wt% to 0.01 wt%, such as 0.5 wt% to 1 .5 wt%.

[0133] In some embodiments, the thermal initiator is present, based on the total weight of the dual curing system, in an amount at least 20 wt% such as at least 30 wt%, such as at least 40 wt%, such as at least 50 wt%, such as at least 60 wt%, such as at least 70 wt%, such as at least 80 wt%.

[0134] In some embodiments, the thermal initiator is present, based on the total weight of the dual curing system, in an amount at most 80 wt%, such as at most 70 wt%, such as at most 60 wt%, such as at most 50 wt%, such as at most 40 wt%, such as at most 30 wt%, such as at most 20 wt%.

[0135] In some embodiments, the thermal initiator is present, based on the total weight of the dual curing system, in an amount from 20 wt% to 80 wt%, such as from 30 wt% to 70 wt%, such as 40 wt% to 60 wt%.

[0136] In some embodiments, the thermal initiator is not pre-added to the UV-curable wind turbine repair resin composition. Instead, the UV-curable wind turbine repair resin composition comprises the free radical photoinitiator and is supplied together with the thermal initiator in a kit. The two components of the dual curing system are therefore separated before they are then combined to produce the UV-curable wind turbine repair resin composition of the first aspect.

[0137] Therefore, in a second aspect of the invention, there is provided a wind turbine repair kit comprising:

[0138] (1) a UV-curable wind turbine repair resin composition comprising: (d) an oligomer having a number average molecular weight Mn of at least 1000, as measured by gel permeation chromatography according to the method provided in the methods section,

[0139] (e) one or more reactive diluent monomers; and

[0140] (f) a free radical photoinitiator for initiating a free radical polymerisation reaction in the UV- curable wind turbine repair resin composition; and

[0141] (2) a thermal initiator for initiating a further free radical polymerisation reaction in the UV-curable wind turbine repair resin composition, wherein the thermal initiator is heat-activatable from the initiation of a free radical polymerisation by the free radical photoinitiator.

[0142] In some embodiments, the thermal initiator is not pre-added into the UV-curable wind turbine repair resin composition to avoid premature decomposition of the thermal initiator, such as in temperatures above ambient temperature. Therefore, the thermal initiator may, in some embodiments, only be added immediately prior to a curing process for wind turbine repair.

[0143] Further components

[0144] The UV-curable wind turbine repair resin composition may further comprise catalysts, inhibitors, stabilisers, and the like. Further possible components may also include antioxidants, acid scavengers, thickeners, flame retardants, silane coupling agents, resin particles, core-shell particle impact modifiers, soluble polymers and block polymers.

[0145] The UV-curable wind turbine repair resin composition may contain a catalyst. When the UV-curable wind turbine repair resin composition is a vinyl ester resin composition as described herein, this may be any catalyst that may facilitate the reaction between the epoxy compound and the chain-extending reagent, in particular the epoxy group and the carboxylic acid group, and the reaction between the lower molecular vinyl ester oligomer and the end-capping reagent.

[0146] Examples of suitable catalysts that can be used herein include tertiary amines such as triethylamine, N',N'-dimethylbenzylamine, N,N-dimethylaniline, 2,4,6-tris(dimethylaminomethyl)phenol, and diazabicyclooctane; quaternary ammonium salts such as trimethylbenzylammonium chloride and methylthiethylammonium chloride; phosphines such as triphenylphosphine (TPP) and tributylphosphine; imidazoles such as 2-methylimidazole, 1 ,2-dimethylimidazole, and 2-ethyl-4-methylimidazole; and triphenylstibine. In some embodiments, the catalyst is triphenyl phosphine (TPP).

[0147] Further examples of suitable catalysts include metal catalysts, such as a chromium complex, for example a chromium(lll) complex or a chromium(VI) complex, and a zinc complex, for example a zinc(l) complex or a zinc(ll) complex. Examples of suitable catalysts include the NACURE series of catalysts from King Industries, Inc., for example NACURE XC-259, the K-PURE series of catalysts, also from King Industries, Inc., for example K-Pure CXC-1765, and the HYCAT series of catalysts from Dimension Technologies Chemical Systems, Inc., for example HYCAT 2000S, HYCAT 3000S and HYCAT OA. The catalyst may be used, based on the total weight of the UV-curable wind turbine repair resin composition, in an amount of from 0.05 wt% to 0.5 wt%.

[0148] The UV-curable wind turbine repair resin composition may contain inhibitors and stabilisers, which help to prolong the shelf life of the product in storage and to control the working time of the adhesive in use. Such inhibitors are well known to those skilled in the art and may comprise quinones, hydroquinones, substituted phenols and the like. Examples of specific inhibitors include, but are not limited to, 2,6-di-tert- butyl-a-dimethylamino-p-cresol, butylated hydroxytoluene (BHT), butylated hydroxyanisole, hydroquinone, toluhydroquinone, para-methoxyphenol, mono tert-butyl hydroquinone, tert-butyl catechol, oxalic acid, and phenothiazine.

[0149] In addition to inhibitors that may be added directly to the UV-curable wind turbine repair resin composition during its preparation, some of the raw materials employed, especially the a,p-unsaturated monocarboxylic acid, (meth)acrylate ester or (meth)acrylate anhydride which may be used to produce a vinyl ester resin composition, may also contain inhibitors introduced by the manufacturer / supplier.

[0150] Hence, on account of the variety of materials that may be chosen, some with in situ inhibitors, and the variety of initiators, promoters and inhibitors that may be used to prepare a composition, the selection of the complete inhibitor package is generally the final step in the formulating process. Preferred combinations of initiator and promoter for the curing system are those suitable for curing at and / or below ambient temperatures.

[0151] The inhibitor may be present, based on the total weight of the UV-curable wind turbine repair resin composition, in an amount of less than 1 .0 wt%, such as less than 0.5 wt%, such as less than 0.1 wt%, such as less than 0.09 wt%, such as less than 0.08 wt%, such as less than 0.07 wt%, such as less than 0.06 wt%.

[0152] Where the UV-curable wind turbine repair resin composition contains inhibitors and stabilisers, the UV- curable wind turbine repair resin composition may further contain diluents for said inhibitors and stabilisers.

[0153] Methods of curing

[0154] The invention also relates to methods of curing the UV-curable wind turbine repair resin composition of the invention.

[0155] Thus, in a fourth aspect of the invention, there is provided a method of curing the UV-curable wind turbine repair resin composition of the first aspect or the second aspect, the method comprising the steps of:

[0156] (i) exposing the UV-curable wind turbine repair resin composition and a free radical photoinitiator to UV light to initiate a cure via a free radical polymerisation, and generating heat in the UV-curable wind turbine repair resin composition; and (ii) exposing the UV-curable wind turbine repair resin composition and a thermal initiator to the heat generated in step (i) to initiate a further cure in the UV-curable wind turbine repair resin composition via the free radical polymerisation.

[0157] In some embodiments, the UV-curable wind turbine repair resin composition is cured at a wavelength of from 200 to 405 nm. Suitably, the UV-curable wind turbine repair resin composition is cured by a source of UV-A light at a wavelength of 315 to 400 nm, UV-B light at a wavelength of 280 to 315 nm, or UV-C light at a wavelength of 200 to 280 nm.

[0158] In some embodiments, the UV light is UV LED light. Therefore, the UV light may be at a wavelength of from 365 to 405 nm, such as from 375 to 405 nm, such as from 385 to 405 nm, such as from 390 to 405 nm.

[0159] In some embodiments, the UV light is at a wavelength from 390 to 405 nm.

[0160] The UV light is preferably obtained from a UV LED lamp. It is to be appreciated that UV LED lamps, such as those commercially available, have a wide range of intensities, and so the curing duration, such as the durations of steps (i) and (ii), may be selected based on the intensity of the UV light emitted from the UV LED lamp.

[0161] In some embodiments, the UV light is obtained from a high-intensity UV LED lamp having an intensity of at least 3.0 W cm2, such as at least 5.0 W cm2, such as at least 10 W cm2, such as at least 15 W cm2, such as at least 20 W cm2, such as at least 25 W cm2, such as at least 30 W cm2.

[0162] In some embodiments, the UV light is obtained from a high-intensity UV LED lamp having an intensity of at most 60 W cm2, such as at most 50 W cm2, such as at most 40 W cm2, such as at most 35 W cm2, such as at most 30 W cm2.

[0163] In some embodiments, the UV light is obtained from a high-intensity UV LED lamp having an intensity of from 3.0 to 60 W cm2, such as at most 5.0 to 50 W cm2, such as 10 to 40 W cm2, such from 15 to 35 W cm2, such as from 15 to 30 W cm2.

[0164] In some embodiments, when the UV light is obtained from a high-intensity UV LED lamp, the duration of step (i) is 120 second or less, such as 90 seconds or less, such as 60 seconds or less, such as 45 seconds or less, such as 30 seconds or less, such as 15 seconds or less.

[0165] In some embodiments, when the UV light is obtained from a high-intensity UV LED lamp, the duration of step (ii) is 120 second or less, such as 90 seconds or less, such as 60 seconds or less, such as 45 seconds or less, such as 30 seconds or less, such as 15 seconds or less.

[0166] In some embodiments, the UV light is obtained from a low-intensity UV LED lamp having an intensity of at least 0.1 W cm2, such as at least 0.2 W cm2, such as at least 0.3 W cm2, such as at least 0.4 W cm2, such as at least 0.5 W cm2, such as at least 0.6 W cm2, such as at least 0.7 W cm2, such as at least 0.8 W cm2, such as at least 0.9 W cm2, such as at least 1 .0 W cm2.

[0167] In some embodiments, the UV light is obtained from a low-intensity UV LED lamp having an intensity of at most 3.0 W cm2, such as at most 2.8 W cm2, such as at most 2.6 W cm2, such as at most 2.4 W cm2, such as at most 2.2 W cm2, such as at most 2.0 W cm2, such as at most 1 .8 W cm2, such as at most 1 .6 W cm2, such as at most 1 .4 W cm2, such as at most 1 .2 W cm2, such as at most 1 .0 W cm2.

[0168] In some embodiments, the UV light is obtained from a low-intensity UV LED lamp having an intensity of from 0.1 to 3.0 W cm2, such as at most 0.2 to 2.8 W cm2, such as 0.3 to 2.6 W cm2, such as from 0.4 to 2.4 W cm2, such as from 0.5 to 2.2 W cm2, such as from 0.6 to 2.0 W cm2, such as from 0.7 to 1 .8 W cm2, such from 0.7 to 1 .6 W cm2, such from 0.7 to 1 .4 W cm2, such from 0.7 to 1 .2 W cm2, such from 0.8 to 1 .2 W cm2, such as from 0.8 to 1 .0 W cm2.

[0169] In some embodiments, when the UV light is obtained from a low-intensity UV LED lamp, the duration of step (i) is 20 minutes or less, such as 18 minutes or less, such as 16 minutes or less, such as 14 minutes or less, such as 12 minutes or less, such as 10 minutes or less.

[0170] In some embodiments, when the UV light is obtained from a low-intensity UV LED lamp, the duration of step (i) is 3 minutes or more, such as 4 minutes or more, such as 5 minutes or more, such as 6 minutes or more, such as 7 minutes or more, such as 8 minutes or more, such as 9 minutes or more, such as 10 minutes or more.

[0171] In some embodiments, when the UV light is obtained from a low-intensity UV LED lamp, the duration of step (i) is from 3 to 20 minutes, such as from 4 to 18 minutes, such as from 5 to 18 minutes, such as from 6 to 16 minutes, such as from 7 to 14 minutes, such as from 8 to 12 minutes.

[0172] In some embodiments, when the UV light is obtained from a low-intensity UV LED lamp, the duration of step (i) is 10 minutes or less.

[0173] In some embodiments, when the UV light is obtained from a low-intensity UV LED lamp, the duration of step (ii) is 30 minutes or less, such as 28 minutes or less, such as 26 minutes or less, such as 24 minutes or less, such as 22 minutes or less, such as 20 minutes or less, such as 18 minutes or less, such as 16 minutes or less, such as 14 minutes or less, such as 12 minutes or less.

[0174] In some embodiments, when the UV light is obtained from a low-intensity UV LED lamp, the duration of step (ii) is 12 minutes or more, such as 14 minutes or more, such as 16 minutes or more, such as 18 minutes or more, such as 20 minutes or more, such as 22 minutes or more, such as 24 minutes or more, such as 26 minutes or more, such as 28 minutes or more, such as 30 minutes or more.

[0175] In some embodiments, when the UV light is obtained from a low-intensity UV LED lamp, the duration of step (ii) is from 12 to 24 minutes, such as from 14 to 22 minutes, such as from 16 to 20 minutes.

[0176] In some embodiments, the UV-curable wind turbine repair resin composition is cured by a mercury lamp, such as a low-pressure mercury lamp, a medium-pressure mercury lamp or a high-pressure mercury lamp.

[0177] In some embodiments, the thermal initiator is exposed to UV light in step (ii). In some embodiments, the UV light source emits heat, such as to increase the temperature of the UV-curable wind turbine repair resin composition. Thus, there may also be a relatively small contribution in initiation from the exposure of the thermal initiator to UV light to due heat generation from the UV light. In alternative embodiments, the thermal initiator is not exposed to UV light in step (ii). Therefore, the UV light source may be removed or switched off after step (i), such that the UV-curable wind turbine repair resin is also not exposed to UV light in step (ii). In such embodiments, the thermal initiator initiates a free radical polymerisation in the UV-curable wind turbine repair resin composition and is induced purely from the heat generation in step (i).

[0178] The temperature achieved in step (ii) from the heat generation in step (i) is a temperature at which the thermal initiator is activated. When the heat generated is sufficient to raise the temperature of at least a portion of the UV-curable wind turbine repair resin composition to activate the thermal initiator, such as above the 1-hour half-life temperature, the 10-hour half-life temperature or the self-accelerating decomposition temperature of the thermal initiator, a deeper cure may be achieved without requiring any further penetration of UV light.

[0179] In some embodiments, the heat generated in step (i) imparts a temperature of at least 70 °C, such as at least 75 °C, such as at least 80 °C, such as at least 85 °C, such as at least 90 °C, such as at least 95 °C, such as at least 100 °C, such as at least 105 °C, such as at least 110 °C, such as at least 115 °C, such as at least 120 °C, such as at least 125 °C, such as at least 130 °C, such as at least 135 °C, such as at least 140 °C, such as at least 145 °C, such as at least 150 °C, to the UV-curable wind turbine repair resin composition.

[0180] In some embodiments, the heat generated in step (i) imparts a temperature from 70 to 150 °C, such as from 80 to 150 °C, such as from 90 to 150 °C.

[0181] The invention also relates to cured products of the UV-curable wind turbine repair resin composition of the first aspect or the second aspect, as described below.

[0182] Wind turbine repair

[0183] The third aspect of the invention relates to the use of the dual curing system of the first aspect or the kit of the second aspect for improving the depth of cure to a UV-curable wind turbine repair resin composition via free radical polymerisation.

[0184] The depth of cure of a wind turbine material is significantly improved for compositions for wind turbines and wind turbine repair, in cases where UV curing alone is insufficient in depth to provide a complete cure. Advantageously, when the dual curing system of the first aspect or the kit of the second aspect is employed, no post-cure process is required which significantly reduces the time and cost for a wind turbine repair process.

[0185] In some embodiments, the use of the dual curing system is conducted according to the method of curing of the fourth aspect.

[0186] A fifth aspect of the invention is a cured product of the UV-curable wind turbine repair resin composition obtained from the method of the fourth aspect. The cured product may have properties as described further below. The sixth of the invention is a wind turbine part comprising the cured product of the fifth aspect. The wind turbine part may be a wind blade part, a tower part or a nacelle part.

[0187] In this aspect, there may be provided an application of a repair patch, comprising the UV-curable wind turbine repair resin composition of the first aspect or the second aspect, for applying on a wind turbine part to cover a damaged portion of the wind turbine. The damaged portion of the wind turbine is typically grinded down and cleaned out. In some embodiments, the repair patch may comprise a plurality of prepregs comprising the UV-curable wind turbine repair resin composition of the first aspect or the second aspect. Therefore, a layered stack of a plurality of prepregs may be applied to form a multilaminar repair patch on the wind turbine part. In some embodiments, the lamination is performed by hand (hand lay-up). Manual smoothing and levelling pressure over the repair patch surface may be employed to spread the resin composition, smooth out and high spots and fill in any low spots in the surface, and to achieve lamination of adjacent prepreg layers with the desired outer surface profile.

[0188] The application of the repair patch for the purposes of repairing a damaged portion of the wind turbine may be performed as a post-production application of a wind turbine part or as an in-field application.

[0189] Mechanical and adhesion properties

[0190] The following properties relate to cured products of the UV-curable wind turbine repair resin composition. For example, the UV-curable wind turbine repair resin composition may be cured by the methods described herein. The sample preparation and testing methodology are discussed further below.

[0191] Typically, when cured, the UV-curable wind turbine repair resin compositions according to the first aspect or the second aspect have the following mechanical properties: a tensile modulus of at least 10000 MPa, such as at least 10200 MPa, such as at least 10400 MPa, such as at least 10600 MPa, such as at least 10800 MPa, such as at least 11000 MPa, such as at least 11200 MPa, such as at least 11400 MPa, such as at least 11600 MPa, wherein the tensile modulus is measured in accordance with the method provided in the methods section; and / or a peak tensile stress of at least 120 MPa, such as at least 122 MPa, such as at least 124 MPa, such as at least 126 MPa, such as at least 128 MPa, such as at least 130 MPa, such as at least 132 MPa, such as at least 134 MPa, such as at least 136 MPa, such as at least 138 MPa, wherein the peak tensile stress is measured in accordance with the method provided in the methods section; and / or a peak tensile strain of at least 2.0%, such as at least 2.1%, such as at least 2.2%, such as at least 2.3%, such as at least 2.4%, such as at least 2.5%, such as at least 2.6%, such as at least 2.7%, wherein the peak tensile strain is measured in accordance with the method provided in the methods section; and / or a flexural modulus of at least 8500 MPa, such as at least 8600 MPa, such as at least 8700 MPa, such as at least 8800 MPa, such as at least 8900 MPa, such as at least 9000 MPa, such as at least 9100 MPa, such as at least 9200 MPa, such as at least 9300 MPa, wherein the flexural modulus is measured in accordance with the method provided in the methods section; and / or a peak flexural stress of at least 215 MPa, such as at least 220 MPa, such as at least 225 MPa, such as at least 230 MPa, such as at least 235 MPa, such as at least 240 MPa, such as at least 245 MPa, such as at least 250 MPa, such as at least 255 MPa, such as at least 260 MPa, wherein the peak flexural stress is measured in accordance with the method provided in the methods section; and / or a peak flexural strain of at least 4.0%, such as at least 4.1 %, such as at least 4.2%, such as at least 4.3%, such as at least 4.4%, such as at least 4.5%, such as at least 4.6%, such as at least 4.7%, wherein the peak flexural strain is measured in accordance with the method provided in the methods section.

[0192] Typically, when cured, the UV-curable wind turbine repair resin compositions according to the first aspect or the second aspect have the following adhesion properties: a z-direction tensile stress at maximum load of at least 7 MPa, such as at least 8 MPa, such as at least 9 MPa, such as at least 10 MPa, such as at least 11 MPa, such as at least 12 MPa, such as at least 13 MPa, wherein the z-direction tensile stress at maximum load is measured in accordance with the method provided in the methods section.

[0193] Typically, when cured, the UV-curable wind turbine repair resin compositions according to the first aspect or the second aspect have a tensile modulus of at least 11000 MPa and a flexural modulus of at least 9000 MPa, wherein the tensile modulus and flexural modulus are each measured in accordance with the methods provided in the methods section.

[0194] Typically, when cured, the UV-curable wind turbine repair resin compositions according to the first aspect or the second aspect have a tensile modulus of at least 11000 MPa, a flexural modulus of at least 9000 MPa, and a z-direction tensile stress at maximum load of at least 10 MPa, wherein the tensile modulus, flexural modulus and z-direction tensile stress at maximum load are each measured in accordance with the methods provided in the methods section.

[0195] Typically, when cured, the UV-curable wind turbine repair resin compositions according to the first aspect or the second aspect have a tensile modulus of at least 11000 MPa, a peak tensile stress of at least 136 MPa, a flexural modulus of at least 9000 MPa, a peak flexural stress of at least 240 MPa, and a z- direction tensile stress at maximum load of at least 10 MPa, wherein the tensile modulus, peak tensile stress, flexural modulus, peak flexural stress and z-direction tensile stress at maximum load are each measured in accordance with the methods provided in the methods section.

[0196] Typically, when cured, the UV-curable wind turbine repair resin compositions according to the first aspect or the second aspect have a tensile modulus of at least 11000 MPa, a peak tensile stress of at least 136 MPa, a peak tensile strain of at least 2.6 %, a flexural modulus of at least 9000 MPa, a peak flexural stress of at least 240 MPa, a peak flexural strain of at least 4.4%, and a z-direction tensile stress at maximum load of at least 10 MPa, wherein the tensile modulus, peak tensile stress, flexural modulus, peak flexural stress, peak flexural strain, and z-direction tensile stress at maximum load are each measured in accordance with the methods provided in the methods section.

[0197] Typically, when cured, the UV-curable wind turbine repair resin compositions according to the first aspect or the second aspect have a tensile modulus of at least 11600 MPa, a peak tensile stress of at least 138 MPa, a peak tensile strain of at least 2.7 %, a flexural modulus of at least 9600 MPa, a peak flexural stress of at least 260 MPa, a peak flexural strain of at least 4.7%, and a z-direction tensile stress at maximum load of at least 12 MPa, wherein the tensile modulus, peak tensile stress, flexural modulus, peak flexural stress, peak flexural strain, and z-direction tensile stress at maximum load are each measured in accordance with the methods provided in the methods section.

[0198] Further embodiments

[0199] In further embodiments, a UV-curable wind turbine repair resin composition according to the first aspect may comprise:

[0200] (a) a UV-curable vinyl ester resin composition comprising a vinyl ester oligomer having a number average molecular weight Mn of at least 1000, as measured by gel permeation chromatography according to the method provided in the methods section, and a reactive diluent monomer; and

[0201] (b) a dual curing system comprising:

[0202] (i) a free radical photoinitiator for initiating a free radical polymerisation reaction in the UV- curable wind turbine repair resin composition; and

[0203] (ii) a thermal initiator for propagating the free radical polymerisation reaction initiated by the free radical photoinitiator in the UV-curable wind turbine repair resin composition.

[0204] In further embodiments, a UV-curable wind turbine repair resin composition according to the first aspect may comprise:

[0205] (a) a UV-curable vinyl ester resin composition comprising a vinyl ester oligomer having a number average molecular weight Mn of at least 2000, as measured by gel permeation chromatography according to the method provided in the methods section; and

[0206] (b) a dual curing system comprising:

[0207] (i) a free radical photoinitiator for initiating a free radical polymerisation reaction in the UV- curable wind turbine repair resin composition; and

[0208] (ii) a thermal initiator for propagating the free radical polymerisation reaction initiated by the free radical photoinitiator in the UV-curable wind turbine repair resin composition. In further embodiments, a UV-curable wind turbine repair resin composition according to the first aspect may comprise:

[0209] (a) a UV-curable vinyl ester resin composition comprising a vinyl ester oligomer having a number average molecular weight Mn of at least 1000, as measured by gel permeation chromatography according to the method provided in the methods section, and a reactive diluent monomer, wherein the vinyl ester oligomer is derived from:

[0210] (i) an epoxy compound comprising at least two epoxy groups;

[0211] (ii) an aromatic chain-extending reagent comprising at least two hydroxyl groups or at least two carboxylic acid groups; and

[0212] (iii) a compound selected from an a,p-unsaturated monocarboxylic acid, a (meth)acrylate ester or a (meth)acrylate anhydride, such as methacrylic acid or methacrylic anhydride; and

[0213] (b) a dual curing system comprising:

[0214] (i) a free radical photoinitiator for initiating a free radical polymerisation reaction in the UV- curable wind turbine repair resin composition; and

[0215] (ii) a thermal initiator for propagating the free radical polymerisation reaction initiated by the free radical photoinitiator in the UV-curable wind turbine repair resin composition.

[0216] In further embodiments, a UV-curable wind turbine repair resin composition according to the second aspect may comprise:

[0217] (a) a vinyl ester oligomer having a number average molecular weight Mn of at least 1000, as measured by gel permeation chromatography according to the method provided in the methods section;

[0218] (b) one or more reactive diluent monomers; and

[0219] (c) a free radical photoinitiator for initiating a free radical polymerisation reaction in the UV- curable wind turbine repair resin composition.

[0220] In further embodiments, a UV-curable wind turbine repair resin composition according to the second aspect may comprise:

[0221] (a) a vinyl ester oligomer having a number average molecular weight Mn of at least 2000, as measured by gel permeation chromatography according to the method provided in the methods section;

[0222] (b) one or more reactive diluent monomers; and (c) a free radical photoinitiator for initiating a free radical polymerisation reaction in the UV- curable wind turbine repair resin composition.

[0223] In further embodiments, a UV-curable wind turbine repair resin composition according to the second aspect may comprise:

[0224] (a) a vinyl ester oligomer having a number average molecular weight Mn of at least 1000, such as at least 2000, as measured by gel permeation chromatography according to the method provided in the methods section; wherein the vinyl ester oligomer is derived from:

[0225] (i) an epoxy compound comprising at least two epoxy groups;

[0226] (ii) an aromatic chain-extending reagent comprising at least two hydroxyl groups or at least two carboxylic acid groups; and

[0227] (iii) a compound selected from an a,p-unsaturated monocarboxylic acid, a (meth)acrylate ester or a (meth)acrylate anhydride, such as methacrylic acid or methacrylic anhydride; and

[0228] (b) one or more reactive diluent monomers; and

[0229] (c) a free radical photoinitiator for initiating a free radical polymerisation reaction in the UV- curable wind turbine repair resin composition.

[0230] ***

[0231] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0232] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0233] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0234] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0235] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0236] It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example + / - 10%.

[0237] Examples

[0238] Materials

[0239] EPIKOTE® 828 is a diglycidyl ether of bisphenol A (DGEBA) prepared from the reaction between bisphenol A and epichlorohydrin obtained from Westlake Epoxy.

[0240] Bisphenol A (BPA) was obtained from Tokyo Chemical Company.

[0241] Triphenyl phosphine (TPP) was obtained from Sigma Aldrich Company Ltd.

[0242] The monofunctional reactive diluent monomer is a mono(meth)acrylate monomer obtained from GEO Speciality Chemicals.

[0243] The difunctional reactive diluent monomer is a di(meth)acrylate monomer obtained from Sartomer.

[0244] The trifunctional reactive diluent monomer is a tri(meth)acrylate monomer obtained from Sartomer

[0245] The photoinitiator was a phosphine oxide photoinitiator obtained from IGM Resins.

[0246] The thermal peroxide was an organic thermal peroxide initiator obtained from Nouryon.

[0247] Methods

[0248] Tensile testing and flexural testing

[0249] Tensile stress and tensile strain properties of the Inventive and Reference Examples were measured according to ISO 527-4 at 5 mm / min.

[0250] Flexural stress and flexural strain properties of the Inventive and Reference Examples were measured according to ISO 14125 / ASTM D790-03 at 2 mm / min.

[0251] The tensile stress at maximum load, also known as the interlaminar tensile strength, is defined as the maximum force required to rupture a specimen across the interlaminar plane per cross sectional area of the specimen at the point of attachment. The z-direction tensile stress at maximum load was measured according to ASTM D1623 at 2 mm / min. A tensile stress was applied so that failure occurs within 60 ± 20 seconds of the initial stress application.

[0252] Number average molecular weight

[0253] The number average molecular weight Mn was measured using gel permeation chromatography in accordance with the following measurement conditions: GPC setup: Viscotex GPC Max, Column Oven, Viscotek VE3580RI detector; GPC software: OmniSec 4.5; Column: Phenomenex Phenogel 5pm Linear / Mixed Guard column 30 x 4.6mm, Phenogel 5pm Linear (2) column 300 x 4.6mm & Phenogel 5pm 50A column 300 x 4.6mm; Mobile phase: THF; Sample; Solvent: THF with 0.2% Toluene as flow marker; Flow rate: 0.35ml / min; Column Temperature: 40°C; Injection volume: 20pL; Detector Temperature: 35°C; Sample Prep: ~0.025g dissolved in 5.0ml Solvent, filtered through a 0.45pm PTFE syringe filter;

[0254] Calibration Standards: Agilent Polystyrene High EasyVials; Elution time: 30 minutes.

[0255] Table 1 - Resin composition

[0256] Table 1 lists the main compositional make-up of an exemplary UV-curable wind turbine repair resin composition before the addition of the dual curing system.

[0257] The UV-curable wind turbine repair resin composition, before the addition of the dual curing system, described in Table 1 below were prepared according to the following general protocol for the production of a vinyl ester resin composition:

[0258] In the first stage, under nitrogen atmosphere, an epoxy compound, a chain-extending reagent and a suitable amount of catalyst (TPP) were weighed into a round bottomed flask with an overhead mechanical stirrer, a gas feed, a temperature probe and in inlet. The reaction mixture was then heated to a temperature of between 120 °C to 130 °C under an inert atmosphere and monitored via melt viscosity and epoxy equivalent weight (EEW) value.

[0259] In the second stage, the temperature was set to 115 °C and a first set of inhibitors were added into the reaction mixture. A gas mixture of 50:50 airmitrogen was then continuously fed into the reactor. The reaction mixture was monitored via melt viscosity and epoxy equivalent weight (EEW) value.

[0260] In the third stage, the end-capping reagent was weighed together with a suitable amount of catalyst (TPP). The temperature of the reaction mixture was set to 100 °C to 125 °C. The mixture containing the end-capping reagent and catalyst is then drip fed over the course of one hour into the reaction mixture. The reaction mixture was monitored via melt viscosity and epoxy equivalent weight (EEW) value.

[0261] In the fourth stage, a second set of inhibitors was added to the reaction mixture. The temperature was set to 80 °C and then the reactive diluent monomer mixture and a third set of inhibitors were added to the reaction mixture under vigorous stirring. The reaction mixture was then cooled to a temperature of between 20 °C to 25 °C (room temperature). Once cooled, the reaction mixture was decanted from the reaction vessel to obtain a vinyl ester resin composition.

[0262] Table 2 - UV-curable wind turbine repair resin composition

[0263] Table 2 lists the main compositional make-up of an exemplary UV-curable wind turbine repair resin composition, which is Composition 1 and comprising the dual curing system of the present invention.

[0264] Discussion of curing results

[0265] Figure 1 shows the degree of cure of glass laminates having a total thickness of 40 layers at various depths of the material (10 layers, 20 layers and 30 layers) as a function of temperature over the curing time. Each glass layer has a thickness of around 1 mm.

[0266] The temperature of the glass laminates was measured using K-type thermocouples which are placed within the layers of the glass laminate construction in order to measure the temperature at 10 layers, 20 layers and 30 layers. The temperatures of the glass laminates at 0 layers and at 40 layers were measured with an infrared thermometer.

[0267] The glass laminates were exposed to UV LED radiation at 395nm using a UV LED lamp which uses Phoseon UV LED Semiconductor Light Matrix Technology obtained from Sadechaf at 60% intensity at 0.8 W cm2for 10 minutes and the temperature is recorded using the K-type thermocouples throughout the curing process. The results demonstrated in Figure 1 demonstrate how the glass laminate is cured at different depths using the dual curing system.

[0268] The first 10 layers (equivalent to a depth of 10 mm) cure rapidly. In less than 1 minute, which is equivalent to the “gel time”, the temperature increased to 90°C, and the temperature peaked at 145°C after 10 minutes, resulting in a total cure time of 10 minutes.

[0269] At a depth of 20 layers (equivalent to a depth of 20 mm), there was an initial induction period, as evidenced by a relatively stable ambient temperature, of around 2 minutes. The break point occurred at around 12 minutes in which the temperature increased to at 90°C, and at around 13 to 14 minutes, the peak temperature increased to 130 to 135°C.

[0270] At a depth of 30 layers (equivalent to a depth of 30 mm), there was a longer induction period of around 5 to 6 minutes. Surprisingly, the break point occurred at 13 minutes at a temperature of 90°C. This was after the UV LED lamp was turned off at 10 minutes. There was nevertheless a continued cure observed, with a curing time of around 18 minutes and a peak temperature achieved of around 135 to 140°C.

[0271] At a depth of 40 layers (equivalent to a depth of 40 mm), there was a continued cure observed. The temperature results are not shown in Figure 1 because a depth of 40 layers corresponds to the bottom layer of the glass laminate. A peak temperature of around 135 to 140°C was achieved, as measured with an infrared thermometer.

[0272] Surprisingly, the results show that, despite the known inability for UV light to penetrate into the material at depths of over 10 layers (around 10 mm), the initiation induced by UV curing with free radical photoinitiator Irgacure 819 causes the next layers of glass to heat up in temperature, thereby activating thermal initiator Trigonox 21 S. Therefore, the results show that curing at a depth of 30 mm, in which there is no UV light penetration, is achieved.

[0273] The dual curing system comprising the combination of a free radical photoinitiator and a thermal initiator performs significantly better, as polymerisation is triggered by UV light, and the combined heat of a UV lamp and the exotherm of the polymerisation reaction consequently triggers the thermal initiator.

[0274] In contrast, the degree of cure of glass laminates achieved using the vinyl ester resin composition of Composition 1 and the free radical photoinitiator alone (in the absence of a thermal initiator) was only 6 layers (around 6 mm). At a depth of 9 layers (around 9 mm), the glass laminates were completely uncured, highlighting the significant limitation in UV cure depth without the use of a thermal initiator.

[0275] Table 2 - Inventive Examples 1 to 2 and Reference Examples 1 to 2

[0276] Inventive Example 1 corresponds to Inventive Composition 1 , and so employs the dual curing system of the first aspect.

[0277] Inventive Example 1 corresponds to Inventive Composition 1 , and so employs the dual curing system of the first aspect, and further includes a step of post-curing for 3 hours at 80 °C. Reference Example 1 corresponds to Inventive Composition 2, without the dual curing system, and instead employs a conventional curing system comprising 2 wt% of a cobalt accelerator and 2 wt% Butanox LPT-IN.

[0278] Reference Example 1 corresponds to Inventive Composition 2, without the dual curing system, and instead employs a conventional curing system comprising 2 wt% of a cobalt accelerator and 2 wt% Butanox LPT-IN, and further includes a step of post-curing for 3 hours at 80 °C.

[0279] In Table 1 below, the notation “• ” indicates a presence of a condition (a post-curing step) and the notation indicates an absence of a condition (a post-curing step).

[0280] As shown in Table 2, the optimum combination of mechanical properties is achieved with Inventive Example 1 , which employs the dual curing system of the present invention and without a post-curing step for 3 hours at 80 °C. That is, Inventive Example 1 achieves a high tensile modulus, peak tensile stress, peak tensile strain, high flexural modulus, peak flexural stress and peak flexural strain. The results show that the use of the dual curing system provides an improved or at least similar combination of mechanical properties compared to Reference Example 1 , which uses a conventional curing system comprising 2 wt% of a cobalt accelerator and 2 wt% Butanox LPT-IN.

[0281] Furthermore, Inventive Example 1 shows that the optimum combination of mechanical properties is achieved without a post-curing step for 3 hours at 80 °C. In contrast, the results from the combination of Reference Examples 1 and 2 show that a post-curing step for 3 hours at 80 °C is required to achieve at most a similar combination of mechanical properties as Inventive Example 1 . Inventive Example 2 shows that a post-curing step for 3 hours at 80 °C has a detrimental effect on the mechanical properties, as the tensile modulus, peak tensile stress, flexural modulus, peak flexural stress and peak flexural strain each decreased relative to Inventive Example 1 after post-curing. Therefore, the optimum combination of mechanical properties, and a deeper cure, is achieved using the dual curing system of the present invention.

Claims

Claims:1 . A UV-curable wind turbine repair resin composition comprising:(a) an oligomer having a number average molecular weight Mn of at least 1000, as measured by gel permeation chromatography according to the method provided in the methods section;(b) one or more reactive diluent monomers; and(c) a dual curing system comprising:(i) a free radical photoinitiator for initiating a free radical polymerisation reaction in the UV- curable wind turbine repair resin composition; and(ii) a thermal initiator for initiating a further free radical polymerisation reaction in the UV-curable wind turbine repair resin composition, wherein the thermal initiator is heat-activatable from the initiation of a free radical polymerisation by the free radical photoinitiator.

2. The UV-curable wind turbine repair resin composition of claim 1 , wherein the free radical photoinitiator is present, based on the total weight of the UV-curable wind turbine repair resin composition, in an amount from 0.1 to 5 wt%.

3. The UV-curable wind turbine repair resin composition of claim 1 or 2, wherein the thermal initiator is present, based on the total weight of the wind turbine repair resin composition, in an amount from 0.1 to 5 wt% .

4. The UV-curable wind turbine repair resin composition of any one of clams 1 to 3, wherein the free radical photoinitiator is present, based on the total weight of the dual curing system, in an amount from 40 to 60 wt%.

5. The UV-curable wind turbine repair resin composition of any one of claims 1 to 4, wherein the thermal initiator is present, based on the total weight of the dual curing system, in an amount from 40 to 60 wt%.

6. The UV-curable wind turbine repair resin composition of any one of claims 1 to 5, wherein the free radical photoinitiator is selected from a phosphine oxide, an aryl ketone, a benzophenone, a hydroxylated ketone, a ketal or a metallocene.

7. The UV-curable wind turbine repair resin composition of any one of claims 1 to 6, wherein the thermal initiator has a 1-hour half-life of 70 °C or less as measured in chlorobenzene and / or a 10-hour half-life of 50 °C or less as measured in chlorobenzene.

8. The UV-curable wind turbine repair resin composition of any one of claims 1 to 7, wherein the thermal initiator has a self-accelerating decomposition temperature (SADT) of 40 °C or less as measured by the Heat Accumulation Storage Test.

9. The UV-curable wind turbine repair resin composition of any one of claims 1 to 8, wherein the free radical photoinitiator is a phosphine oxide.

10. The UV-curable wind turbine repair resin composition of any one of claims 1 to 9, wherein the thermal initiator is a thermal peroxide, such as an organic thermal peroxide.

11. The UV-curable wind turbine repair resin composition of any one of claims 1 to 10, wherein the thermal initiator is a thermal perester peroxide.

12. The UV-curable wind turbine repair resin composition of any one of claims 1 to 11 , wherein the oligomer has a number average molecular weight Mn of at least 2000, as measured by gel permeation chromatography according to the method provided in the methods section.

13. The UV-curable wind turbine repair resin composition of any one of claims 1 to 12, wherein the UV- curable wind turbine repair resin composition is a vinyl ester resin composition comprising a vinyl ester oligomer and a reactive diluent monomer.

14. The UV-curable wind turbine repair resin composition of claim 13, wherein the vinyl ester oligomer is derived from:(i) an epoxy compound comprising at least two epoxy groups;(ii) an aromatic chain-extending reagent comprising at least two hydroxyl groups or at least two carboxylic acid groups; and(iii) a compound selected from an a,p-unsaturated monocarboxylic acid, a (meth)acrylate ester or a (meth)acrylate anhydride, such as methacrylic acid.

15. The UV-curable wind turbine repair resin composition of any one of claims 1 to 14, wherein the one or more reactive diluent monomers is a monofunctional acrylate and a polyfunctional methacrylate.

16. The UV-curable wind turbine repair resin composition of any one of claims 1 to 15, further comprising a vinyl ester trimer, optionally wherein the vinyl ester trimer has a molecular weight of at least 500, as measured by gel permeation chromatography according to the method provided in the methods section.

17. A wind turbine repair kit comprising:(1) a UV-curable wind turbine repair resin composition comprising:(a) an oligomer having a number average molecular weight Mn of at least 1000, as measured by gel permeation chromatography as measured by gel permeation chromatography according to the method provided in the methods section;(b) one or more reactive diluent monomers; and(c) a free radical photoinitiator for initiating a free radical polymerisation reaction in the UV- curable wind turbine repair resin composition; and(2) a thermal initiator for initiating a further free radical polymerisation reaction in the UV-curable wind turbine repair resin composition, wherein the thermal initiator is heat-activatable from the initiation of a free radical polymerisation by the free radical photoinitiator.

18. Use of the dual curing system of any one of claims 1 to 16 or the kit of claim 17 for improving the depth of cure to a UV-curable wind turbine repair resin composition via free radical polymerisation.

19. A method of curing the UV-curable wind turbine repair resin composition of any one of claims 1 to 17, the method comprising the steps of:(i) exposing the UV-curable wind turbine repair resin composition and a free radical photoinitiator to UV light to initiate a cure via a free radical polymerisation, and generating heat in the UV-curable wind turbine repair resin composition; and(ii) exposing the UV-curable wind turbine repair resin composition and a thermal initiator to the heat generated in step (i) to initiate a further cure in the UV-curable wind turbine repair resin composition via the free radical polymerisation.

20. The method of claim 19, wherein the UV light is at a wavelength from 200 to 405 nm, such as from 390 to 405 nm.

21. The method of claim 19 or 20, wherein the duration of step (i) is less than 120 seconds.

22. The method of any one of claims 19 to 21 , wherein the thermal initiator is exposed to UV light in step (ii).

23. The method of any one of claims 19 to 22, wherein the heat generated in step (i) imparts a temperature from 90 to 150 °C to the UV-curable wind turbine repair resin composition.

24. A cured product of the UV-curable wind turbine repair resin composition, the cured product obtained from the method of any one of claims 19 to 23.

25. A wind turbine part comprising the cured product of claim 24.

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