Elongate reinforcing structure for a wind turbine blade

Abstract

Herein is described an elongate reinforcing structure comprising a pultruded plank having a surface to which thermoplastic binder particles are adhered.

Description

[0001] Elongate reinforcing structure for a wind turbine blade

[0002] Field of the Invention

[0003] The present invention relates to elongate reinforcing structures for wind turbine blades and processes for producing elongate reinforcing structures for wind turbine blades, for example and elongate reinforcing structures comprising a pultruded plank.

[0004] Background

[0005] It is known to use reinforcing materials containing reinforcing fibers, for example in the form of pultruded planks, to reinforce structural components, such as wind turbine blades or related components such as a spar cap. These structural components are often formed by laying pultruded planks into a mold, filling the mold with a resin, and curing the resin to form a structural component.

[0006] Several layers of reinforcing material containing reinforcing fibers, for example in the form of pultruded planks, may be required to form a structural component, for example a section of a wind turbine blade. Due to the pultrusion process used for forming the pultruded planks, pultruded planks generally have a very smooth surface. Conventionally, a peel-ply layer is applied to the surface of the pultruded plank during manufacturing of the pultruded plank to ensure the pultruded plank has a textured surface after removal of the peel-ply layer before assembly of the pultruded planks into a structural component. The peel-ply layers are used to leave behind a textured surface on the pultruded plank after removal of the peel-ply layer from the surface of the pultruded plank in order to attempt to aid resin infusion between stacked pultruded planks.

[0007] There is a need to provide improved elongate reinforcing structures, such as pultruded planks, and associated processes to provide improved structural components and improvements in the production of structural components such as components of wind turbine blades, e.g., spar caps.

[0008] Summary of the Invention

[0009] At its most general, the present invention provides an elongate reinforcing structure comprising a pultruded plank having a surface to which thermoplastic binder particles are adhered. In embodiments, the thermoplastic binder particles have a glass transition temperature, melting temperature or softening point as described herein. For example, the thermoplastic binder particles may have a glass transition temperature of up to about 100 °C. In an aspect, the present invention provides an elongate reinforcing structure for a wind turbine blade, the elongate reinforcing structure comprising: a pultruded plank comprising glass reinforcing fibers and a thermoset resin, the pultruded plank having a surface; and thermoplastic binder particles adhered to the surface of the pultruded plank.

[0010] In an aspect, the present invention provides a process for producing an elongate reinforcing structure for a wind turbine blade, the process comprising: drawing glass reinforcing fibers and a thermosetting resin through a pultrusion die to form a pultruded plank at a pultrusion die outlet; and applying thermoplastic binder particles to a surface of the pultruded plank.

[0011] In an aspect, the present invention provides a process for producing an elongate reinforcing structure for a wind turbine blade, the process comprising: drawing glass reinforcing fibers and a thermosetting resin through a pultrusion die to form a pultruded plank at a pultrusion die outlet; applying thermoplastic binder particles to a surface of the pultruded plank; and adhering the thermoplastic binder particles to a surface of the pultruded plank.

[0012] In an aspect, the present invention provides a wind turbine blade comprising an elongate reinforcing structure as described herein.

[0013] In an aspect, the present invention provides an elongate reinforcing structure for a wind turbine blade obtainable or obtained by the process described herein.

[0014] The present inventors have found that conventional techniques to provide a pultruded plank with a textured surface by using peel-ply layers cause difficulties in assembling structural components from pultruded planks due to the need to remove the peel-ply layers. Removal of the peel-ply layers in order to expose the textured surface of the pultruded plank surface also produces waste which the present inventors seek to avoid.

[0015] The present inventors have found that the present invention provides improvements in the efficiency of producing elongate reinforcing structures for wind turbine blades and the assembly of structural components for wind turbine blades. In particular, the present inventors have found that the present invention removes the need for employing peel-ply layers on pultruded planks as the elongate reinforcing structures defined herein are provided with a textured surface on the pultruded plank by the thermoplastic binder particles adhered to a surface of the pultruded plank. The present invention also provides a solution to the problem of the waste associated with conventional peel-ply layers.

[0016] The present inventors have surprisingly found that the elongate reinforcing structures of the present invention can be efficiently produced either: by applying the thermoplastic binder described herein to the pultruded plank following the exit of the pultruded plank from a pultrusion die such that the temperature of the pultruded plank on extrusion form the die causes the thermoplastic binder to at least partially soften / melt so that the thermoplastic binder adheres to the pultruded plank on cooling of the pultruded plank and the thermoplastic binder; or by applying the thermoplastic binder to an already cooled pultruded plank and heating the thermoplastic binder to at least partially soften / melt so that the thermoplastic binder adheres to the pultruded plank on cooling of the pultruded plank and the thermoplastic binder.

[0017] The present inventors have also found that by employing a thermoplastic binder (for example, a thermoplastic binder having a low glass transition temperature of up to about 100 °C) as described herein, the thermoplastic binder can be at least at least partially soften / melt without damaging the pultruded plank. Therefore, the thermoplastic binder adhered to a surface of the pultruded plank can also be reactivated, if required, by heating without damaging the pultruded plank.

[0018] The present inventors have also found that the elongate reinforcing structures described herein have also been found to surprisingly improve the efficiency in the production of structural components, such as structural components of wind turbine blades. The elongate reinforcing structures described herein have also be found to exhibit excellent handleability, in particular the elongate reinforcing structures can be rolled, cut and stacked without shedding binder. Even more surprisingly, the present inventors have found that the elongate reinforcing structures described herein can provide improvements in the efficiency of the production of reinforced structural components, e.g. wind turbine blades, without detrimentally effecting the mechanical properties of the final components.

[0019] The invention includes the combination of the aspects, embodiments and preferred features described herein except where such a combination is clearly impermissible or expressly avoided. Brief Description of the Figures

[0020] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0021] Figure 1 is a graph showing the particle size distribution of examples of thermoplastic binder particles that may be applied to a pultruded plank produce an elongate reinforcing structure as described herein; and

[0022] Figure 2 is a photograph of an elongate reinforcing structure described herein.

[0023] Detailed Description

[0024] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art.

[0025] Described herein is an elongate reinforcing structure for a wind turbine blade comprising a pultruded plank having a thermoplastic binder adhered to a surface of the pultruded plank.

[0026] Pultruded Plank

[0027] Pultruded planks are produced by drawing reinforcing fibers and a resin through a pultrusion die. Generally, pultruded planks are produced by drawing reinforcing fibers and a thermosetting resin through a pultrusion die.

[0028] Pultruded planks contain reinforcing fibers arranged substantially parallel to the length of the pultruded plank.

[0029] In preferred embodiments, the reinforcing fibers of the pultruded planks comprise, consist essentially of, or consist of glass fibers.

[0030] In embodiments, the pultruded plank comprises, consists essentially of, or consists of reinforcing fibers and a resin. In embodiments, the pultruded plank comprises, consists essentially of, or consists of glass reinforcing fibers and a thermoset resin.

[0031] In embodiments, the reinforcing fibers (e.g., glass fibers) constitute from about 55 wt.% to about 95 wt.% by total weight of the pultruded plank, and the resin (e.g., the thermoset resin) constitutes from about 5 wt.% to about 45 wt.% of the pultruded plank. For example, the reinforcing fibers (e.g., glass fibers) may constitute from about 70 wt.% to about 90 wt.% by total weight of the pultruded plank, and the resin (e.g., the thermoset resin) may constitutes from about 10 wt.% to about 30 wt.% of the pultruded plank.

[0032] The term "glass fibers" is used herein to refer to a plurality of continuous glass filaments (the term "continuous" as used here is used to refer to a fiber / filament that has a length many times longer than its diameter, for example at least about 5000 times longer than its diameter, e.g., at least about 10 000 times longer than its diameter). The glass fibers used in the pultruded planks described herein may be provided as glass fiber strands (or tows). The glass fibers may be formed by a continuous manufacturing process in which molten glass passes through the holes of a "bushing," the streams of molten glass thereby formed are solidified into filaments / fibers. The glass fibers described herein may include a sizing on their surface, e.g., a sizing applied on the glass fibers during formation of the fibers. The sizing can include components such as a film former, lubricant, coupling agent (to promote compatibility between the glass fibers and the resin used to form a pultruded plank), etc. that facilitate formation of the glass fibers and / or use thereof in a matrix resin. In some embodiments, the glass fibers include a polyester compatible sizing, an epoxy compatible sizing, or a vinyl-ester compatible sizing.

[0033] The term "glass fiber strand" or "glass fiber tow" as used herein, refers to a bundle of continuous glass filaments. In embodiments the glass fiber strands or tows are bundles of untwisted glass filaments.

[0034] In embodiments, glass fiber strands or glass fiber tows are provided from glass fiber direct rovings. Glass fiber direct rovings are made up of a bundle of continuous untwisted (i.e., substantially parallel, or parallel) glass filaments bonded (as the glass filaments are formed) into a single strand and wound onto a bobbin.

[0035] Any suitable glass reinforcing fibers may be employed, for example, fibers made from E glass, E-CR glass (such as Advantex™ glass fibers available from Owens Corning), C glass, H glass, S glass, and AR glass types can be used.

[0036] In embodiments, the glass fibers referred to herein have a linear mass density in the range of about 50 Tex to about 5000 Tex, for example about 200 Tex to about 4800 Tex, about 500 Tex to about 4800 Tex, aboutlOOO Tex to about 4800 Tex, or about 2000 Tex to about 4800 Tex. In embodiments, the pultruded planks described herein may comprise additional fibers in addition to glass fibers. Examples of other fibers which may be included include carbon fibres and / or polymer fibers and / or natural fibers. n embodiments, the resin is a thermoset resin, for example a suitable thermoset resin. Examples of suitable resins include an epoxy resin, a polyester resin or a vinyl-ester resin.

[0037] The pultruded planks described herein have a length, a width and a thickness. The length of the pultruded plank is greater than the width of the pultruded plank and the thickness of the pultruded plank, and the width of the pultruded plank is greater than the thickness of the pultruded plank. The pultruded planks may upper and lower surfaces.

[0038] The pultruded plank may have a length in the range of about 1 m to about 1000 m, for example about 2 m to about 500 m, about 5 m to about 250 m, or about 10 m to about 100 m.

[0039] The pultruded plank may have a width in the range of about 2 cm to about 50 cm, for example about 5 cm to about 20 cm, or about 5 cm to about 15 cm.

[0040] In embodiments, the pultruded plank has a thickness in the range of about 1 mm to about 10 mm, for example about 2 mm to about 8 mm, or about 3 mm to about 5 mm.

[0041] Thermoplastic Binder

[0042] The elongate reinforcing structure comprises a thermoplastic binder.

[0043] In embodiments, the thermoplastic binder of the elongate reinforcing structure may be applied to the pultruded plank in the form of thermoplastic binder particles (which may also be described as powder binder particles).

[0044] In embodiments, the elongate reinforcing structure may be described herein as comprising a pultruded plank with thermoplastic binder particles adhered to a surface of the pultruded plank. In embodiments, the elongate reinforcing structure can be described as comprising a pultruded plank having a homogenous distribution of thermoplastic binder particles adhered to a surface of the pultruded plank.

[0045] In embodiments, the thermoplastic binder (e.g. thermoplastic binder particles) comprises, consists essentially of, or consists of a thermoplastic resin. In embodiments, the thermoplastic binder (e.g. thermoplastic binder particles) comprises or is composed of a thermoplastic resin selected from an epoxy resin, an acrylate resin, or a polyester resin. In embodiments, the thermoplastic binder (e.g. thermoplastic binder particles) comprises or is composed of a thermoplastic resin selected from an epoxy resin or a polyester resin. In embodiments, the thermoplastic binder comprises or consists of a resin comprising epoxy, acrylate, or ester functional groups, for example a resin comprising epoxy, or ester functional groups. In embodiments, the thermoplastic binder (e.g. thermoplastic binder particles) comprises or consists of a biobased resin, for example a biobased resin comprising epoxy, acrylate, or ester functional groups, for example a biobased resin comprising epoxy, or ester functional groups.

[0046] In embodiments, the thermoplastic binder (e.g. thermoplastic binder particles) has a glass transition temperature of up to about 220 °C, for example up to about 200 °C, up to about 180 °C, up to about 160 °C, up to about 140 °C, up to about 120 °C, up to about 100 °C, up to about 90 °C, up to about 80 °C, up to about 75 °C, up to about 70 °C, up to about 65 °C, up to about 60 °C, or up to about 55 °C. In embodiments, the thermoplastic binder has a glass transition temperature of at least about 30 °C, for example at least about 35 °C, or at least about 40 °C. In embodiments, the thermoplastic binder has a glass transition temperature in the range of about 30 °C to about 220 °C, for example about 40 °C to about 150 °C, about 40 °C to about 120 °C, about 40 °C to about 120 °C, about 40 °C to about 75 °C, or about 40 °C to about 70 °C. The glass transition temperature of the thermoplastic binder may be determined using differential scanning calorimetry (DSC) according to EN ISO 11357-2 (determination of glass transition temperature). The glass transition temperature of the binder may be determined using differential scanning calorimetry (DSC) according to EN ISO 11357-2 (determination of glass transition temperature) wherein the glass transition temperature is determined as the value provided on the second heating cycle. The glass transition temperature of the thermoplastic binder may be determined according to the EN ISO 11357-2 test method by heating the thermoplastic binder under an air flow of 80 mL / min at a heating rate of lOK / min, heating from - 60 °C to 300 °C, or for example - 60 °C to 120 °C. In embodiments, the glass transition temperature of the thermoplastic binder may be determined according to the EN ISO 11357-2 test method by heating the thermoplastic binder under an air flow of 80 mL / min at a heating rate of lOK / min, heating from - 60 °C to 300 °C, or for example - 60 °C to 120 °C, and then holding for 5 mins at 300 °C, or for example - 60 °C to 120 °C, before cooling from 300 °C to - 60 °C at a cooling rate of lOK / min and then holding for 5 mins at - 60 °C before heating from - 60 °C to 300 °C, or for example - 60 °C to 120 °C, again at a heating rate of lOK / min and the glass transition temperature is determined as the value provided on the second heating cycle. In embodiments, the thermoplastic binder (e.g. thermoplastic binder particles) has a melting point such that the binder is completely molten when exposed to a temperature of up to about 220 °C for at least suitable time period, for example when exposed to a temperature of up to about 200 °C for at least suitable time period, when exposed to a temperature of up to about 150 °C for at least suitable time period , when exposed to a temperature of up to about 100 °C for at least suitable time period , or when exposed to a temperature of up to about 90 °C for at least suitable time period. In embodiments, the binder has a melting point such that the binder is completely molten when exposed to a temperature in the range of about 60 °C to about 220 °C, for example about 80 °C to about 150 °C for at least suitable time period. The suitable time period may be up to 1 hour, for example up to 30 mins. The suitable time period may be at least about 1 min, for example, at least about 5 mins or at least about 10 mins.

[0047] In embodiments, the thermoplastic binder (e.g. thermoplastic binder particles) has a softening temperature in the range of about 50°C to about 200 °C, for example about 60°C to about 150 °C. In embodiments, the softening temperature may be determined using an oscillatory rheometer at 0.1% deformation in plan-plan geometry, a frequency of 1 Hz with a binder sample having a thickness of 400 pm and diameter of 25 mm, employing a heating-cooling-heating cycle which heats from 30°C-200°C at a rate of 3°C / min, cooling from 200°C-30°C and heating from 30°C-200°C at a rate of 3°C / min. The softening temperature is taken during the first heating.

[0048] In embodiments, the thermoplastic binder is applied to the pultruded plank as binder particles. The binder particles before being applied to the pultruded plank may have a volume average particle size of up to about 1 mm, for example up to about 800 pm, up to about 600 pm, up to about 500 pm, up to about 400 pm, up to about 300 pm, or up to about 200 pm. In embodiments, the binder particles before being applied to the pultruded plank have a volume average particle size of greater than about 10 pm, for example greater than about 20 pm, greater than about 30 pm, greater than about 40 pm, or greater than about 50 pm. In embodiments, the binder particles before being applied to the pultruded plank have a volume average particle size in the range of about 10 pm to about 1mm, for example about 20 pm to about 600 pm, about 30 pm to about 500 pm, about 40 pm to about 400 pm, or about 50 pm to about 300 pm. The volume average particle size of the binder particles before being applied to the pultruded plank may be determined using a dynamic light scattering technique on a dispersion of the binder particles. A Particle size analyzer such as a LS13320 Particle Size Analyzer from Beckman™ may be employed to determine the volume average particle size by laser diffraction following the ISO 13320 2009 norm (i.e. using a dynamic light scattering technique on a dispersion of the binder particles before being applied to the pultruded plank). The samples may be analyzed twice, as received, after dispersion in air and the sample quantity is typically around 20 g per test.

[0049] In embodiments, the thermoplastic binder of the elongate reinforcing structure can be described as thermoplastic binder particles. The thermoplastic binder particles applied to the pultruded plank may be adhered to a surface of the pultruded plank such that the elongate reinforcing structure comprises thermoplastic binder particles adhered to a surface. The thermoplastic binder particles applied to the surface of a pultruded plank may be adhered to the pultruded plank to form elongate reinforcing structure.

[0050] In embodiments, the thermoplastic binder (e.g. thermoplastic binder particles) has a shear modulus, G, at 30 °C in the range of about 5 to about 50 Mpa, for example about 5 to about 40 Mpa, or about 7 to about 30 Mpa. The shear modulus, G, at 30 °C of the binder may be determined using an oscillatory rheometer at 0.1% deformation in plan-plan geometry, a frequency of 1 Hz with a binder sample having a thickness of 400 pm and diameter of 25 mm, employing a heating- cooling-heating cycle which heats from 30°C-130°C at a rate of 3°C / min, cooling from 130°C-30°C and heating from 30°C-130°C at a rate of 3°C / min.

[0051] In embodiments, the thermoplastic binder (e.g. thermoplastic binder particles) has a dynamic viscosity, q, at 130 °C in the range of about 1 to about 400 Pa.s, for example about 10 to about 400 Pa.s. The dynamic viscosity, q, at 130 °C of the binder may be determined using an oscillatory rheometer at 0.1% deformation in plan-plan geometry, a frequency of 1 Hz with a binder sample having a thickness of 400 pm and diameter of 25 mm, employing a heating-cooling-heating cycle which heats from 30°C-130°C at a rate of 3°C / min, cooling from 130°C-30°C and heating from 30°C- 130°C at a rate of 3°C / min.

[0052] In embodiments, the thermoplastic binder (e.g., thermoplastic binder particles) comprises or is composed of a resin comprising epoxy functional groups, for example the binder may be an epoxy resin. In embodiments, the thermoplastic binder comprises or is composed of an epoxy resin having a molecular weight, Mw, in the range of about 2000 to about 6000, for example about 3000 to about 6000, about 4000 to about 6000, or about 4500 to about 5500. In embodiments, the binder comprises or is composed of an epoxy resin having a molecular weight, Mw, in the range of about 2000 to about 6000 and a polydispersity in the range of 1 to 5, for example 2 to 4, 2 to 3 or 2.5 to 3 (where polydispersity is calculated as Mw / Mn). In embodiments, the thermoplastic binder comprises or is composed of an epoxy resin and the epoxy resin is an epoxylated BPA or an epoxy novalac. In embodiments, the thermoplastic binder comprises or is composed of an epoxy resin and the epoxy resin is an epoxylated BPA.

[0053] In embodiments, the thermoplastic binder (e.g., thermoplastic binder particles) comprises or is composed of a resin comprising ester functional groups, for example the binder may be a polyester resin. In embodiments, the binder comprises or is composed of a polyester resin having a molecular weight, MW, in the range of about 1000 to about 300000. In embodiments, the thermoplastic binder comprises or is composed of an unsaturated polyester resin, for example an aromatic unsaturated polyester resin or an aliphatic unsaturated polyester resin. Examples of suitable polyester-based resins include BPA polyesters such as BPA fumarate polyesters, for example alkoxylated (e.g., ethoxylated or propoxylated) BPA fumarate polyesters.

[0054] In embodiments, the thermoplastic binder particles may be applied to the pultruded plank in the form of thermoplastic binder particles (which may also be described as powder thermoplastic binder), a dispersion comprising the thermoplastic binder or a solution comprising the thermoplastic binder. In embodiments, the thermoplastic binder particles may be applied to the pultruded plank by spraying.

[0055] Elongate Reinforcing structure

[0056] The elongate reinforcing structure of the invention comprises a pultruded plank as described herein and thermoplastic binder (e.g., thermoplastic binder particles) as described herein.

[0057] In embodiments, the reinforcing fibers (for example, glass fibers) constitute at least about 40 wt.% of the elongate reinforcing structure, for example at least about 50 wt.% of the elongate reinforcing structure, or at least about 60 wt.% of the elongate reinforcing structure. In embodiments, the reinforcing fibers (for example, glass fibers) constitute from about 40 wt.% to about 85 wt.% of the elongate reinforcing structure, for example from about 50 wt.% to about 85 wt.% of the elongate reinforcing structure.

[0058] In embodiments, the resin (for example, thermoset resin) constitutes at least about 10 wt.% of the elongate reinforcing structure, for example at least about 15 wt.% of the elongate reinforcing structure. In embodiments, the thermoset resin (for example, glass fibers) constitutes from about 10 wt.% to about 50 wt.% of the elongate reinforcing structure, for example about 15 wt.% to about 40 wt.% of the elongate reinforcing structure. In embodiments, the elongate reinforcing structure comprises a pultruded plank comprising glass reinforcing fibers and a thermoset resin with a thermoplastic binder adhered to the surface of the pultruded plank, the glass reinforcing fibers of the pultruded plank constituting at least about 50 wt.% of the elongate reinforcing structure; the thermoset resin constituting at least about 10 wt.% of the elongate reinforcing structure; and wherein the thermoplastic binder particles are adhered to a surface of the pultruded plank in an amount of at least about 5 g / m2, for example in a range of about 5 g / m2to about 100 g / m2of.

[0059] In embodiments, the elongate reinforcing structure can be described as comprising a pultruded plank having a homogenous distribution of thermoplastic binder particles adhered to a surface of the pultruded plank. In embodiments, the elongate reinforcing structure comprises up to about 100 g / m2of the thermoplastic binder (e.g., thermoplastic binder particles), for example, up to about 50 g / m2, up to about 40 g / m2, up to about 30 g / m2, or up to about 20 g / m2of the thermoplastic binder. In embodiments, the elongate reinforcing structure comprises at least about 5 g / m2of the thermoplastic binder, for example at least about 10 g / m2of the thermoplastic binder. In embodiments, the elongate reinforcing structure comprises from about 5 g / m2to about 100 g / m2of the thermoplastic binder, for example about 5 g / m2to about 50 g / m2, about 10 g / m2to about 50 g / m2, or about 10 g / m2to about 30 g / m2of the thermoplastic binder.

[0060] The elongate reinforcing structure comprises thermoplastic binder (e.g., thermoplastic binder particles) adhered to a surface of a pultruded plank. In embodiments, the elongate reinforcing structure may comprise a pultruded plank having thermoplastic binder adhered to both surfaces (upper and lower surfaces) of the pultruded plank. In embodiments, the elongate reinforcing structure may comprise a pultruded plank having thermoplastic binder adhered to only the upper or lower surface of the pultruded plank. For example, the elongate reinforcing structure may comprise a pultruded plank having thermoplastic binder adhered to one surface of the pultruded plank, the other surface of the pultruded plank being substantially free of thermoplastic binder (for example a surface comprising less than about 1 g / m2, for example less than about 0.5 g / m2, or less than about 0.1 g / m2, of thermoplastic binder).

[0061] The elongate reinforcing structure comprises a pultruded plank and thermoplastic binder (e.g., thermoplastic binder particles) adhered to the pultruded plank. In embodiments, the thermoplastic binder may be adhered to the pultruded plank by heating of the thermoplastic binder. In embodiments the thermoplastic binder is adhered to a surface of the pultruded plank by being heated such that the binder melts or at least partially melts, for example at least partially melt on a surface of the pultruded plank. For example, the elongate reinforcing structure may comprise solid thermoplastic binder, for example solid thermoplastic binder particles, adhered to the pultruded plank, wherein the thermoplastic binder, for example thermoplastic binder particles, applied to the pultruded plank have previously been softened or at least partially melted.

[0062] In embodiments, the elongate reinforcing structure comprises discrete areas of thermoplastic binder (may be referred to as binder particles or distinct binder particles) on the surface of the pultruded plank. In embodiments, the elongate reinforcing structure can be described as comprising a pultruded plank having a homogenous distribution of thermoplastic binder particles adhered to a surface of the pultruded plank. Figure 2 is photograph of an example of an elongate reinforcing structure as described herein, it can be seen that binder particles applied to the surface of a pultruded plank which were then melted and solidified have not coagulated to form a layer over the pultruded plank surface but instead can be seen as thermoplastic binder particles (i.e., distinct binder particles). The terms "distinct binder particles" or "discrete binder particles" may be used herein to describe thermoplastic binder particles adhered to pultruded plank having a size distribution as described herein. As described above, the terms "distinct binder particles" and "discrete binder particles" are used herein to refer to thermoplastic binder particles adhered to the surface of the pultruded plank being spaced apart from one another, that is around each thermoplastic binder particle there is an area of the surface of the pultruded plank that is free from thermoplastic binder particles. In embodiments in which the resin is a thermoplastic resin, there may be an area of the surface of the pultruded plank around each thermoplastic binder particle that is free from thermoplastic binder.

[0063] The present inventors have found that the elongate reinforcing structures described herein which comprise a pultruded plank with thermoplastic binder (e.g., binder particles) adhered to the pultruded plank (can be described as comprising pultruded planks having a surface to which thermoplastic binder (e.g., binder particles) is permanently adhered. The term "permanently adhered" is used herein to refer to thermoplastic binder (e.g., binder particles) that cannot be removed from the pultruded planks by abrasion. The thermoplastic binder (e.g., binder particles) may be permanently adhered to a surface of the pultruded plank by softening or at least partially melting the thermoplastic binder on the surface of the pultruded plank as described herein. For example, thermoplastic binder is considered to be permanently adhered to a surface of a pultruded plank, if following a scrub test carried out according to ISO 11998-2006 (using Elcometer 1720 Abrasion Tester) without liquid and using a microfiber fabric or a Scotch-Brite™ 7446 type pad as the abrasive pad (weight of abrasive pad with holder being 455 g, scrubbed surface being 300 mm long, performing 200 runs (back and forth)) no impact on binder adhesion is observed and no weight loss occurs.

[0064] In embodiments, the elongate reinforcing structure comprises a pultruded plank with thermoplastic binder particles adhered to the pultruded plank, the thermoplastic binder particles forming distinct binder particles on a surface of the pultruded plank (for example, as opposed to the binder coagulating to form large patches or a layer over the surface of the pultruded plank). The terms "distinct binder particles" and "discrete binder particles" are used herein to refer to binder particles adhered to the surface of the pultruded plank being spaced apart from one another, that is around each binder particle there is an area of the surface of the pultruded plank that is free from thermoplastic binder. In embodiments, the thermoplastic binder particles adhered to a surface of the pultruded plank have a longest axial length of less than about 2mm, for example less than about 1 mm.

[0065] In embodiments, the thermoplastic binder particles adhered to a surface of the elongate reinforcing structure have a size distribution such that at least about 90 wt.% of the thermoplastic binder particles adhered to a surface of the pultruded plank have a longest axial length of less than about 2mm, for example, less than about 1 mm, less than about 800 pm, less than about 700 pm, less than about 600 pm, or less than about 500 pm. In embodiments, the thermoplastic binder particles adhered to a surface of the elongate reinforcing structure have a size distribution such that the thermoplastic binder particles adhered to a surface of the pultruded plank have a longest axial length of at least about 1 pm, at least about 10 pm, or at least about 20 pm. In embodiments, the thermoplastic binder particles adhered to a surface of the elongate reinforcing structure have a size distribution such that at least about 90 wt.% of the thermoplastic binder particles adhered to a surface of the pultruded plank have a longest axial length of at least about 1 pm, at least about 10 pm, or at least about 20 pm.

[0066] In embodiments, the thermoplastic binder particles adhered to a surface of the elongate reinforcing structure have a size distribution such that the thermoplastic binder particles adhered to a surface of the pultruded plank have a longest axial length in the range of about 1 pm to about 1 mm, for example in the range of about 1 pm to about 800 pm.

[0067] In embodiments, the thermoplastic binder particles adhered to a surface of the elongate reinforcing structure have a size distribution such that at least about 90 wt.% of the thermoplastic binder particles adhered to a surface of the pultruded plank have a longest axial length in the range of about 1 pm to about 1 mm, for example in the range of about 1 pm to about 800 pm, about 10 pm to about 600 pm, or about 10 pm to about 500 pm.

[0068] In embodiments, the thermoplastic binder particles adhered to a surface of the elongate reinforcing structure have a size distribution such that at least 90% of the thermoplastic binder particles (by number of particles) adhered to a surface of the pultruded plank have a longest axial length of less than about 2mm, for example, less than about 1 mm, less than about 800 pm, less than about 700 pm, less than about 600 pm, or less than about 500 pm. In embodiments, the thermoplastic binder particles adhered to a surface of the elongate reinforcing structure have a size distribution such that at least 90% of the thermoplastic binder particles (by number of particles) adhered to a surface of the pultruded plank have a longest axial length of at least about 1 pm, at least about 10 pm, or at least about 20 pm. In embodiments, the thermoplastic binder particles adhered to a surface of the elongate reinforcing structure have a size distribution such that at least 90% of the thermoplastic binder particles (by number of particles) adhered to a surface of the pultruded plank have a longest axial length in the range of about 1 pm to about 1 mm, for example in the range of about 1 pm to about 800 pm, about 10 pm to about 600 pm, or about 10 pm to about 500 pm.

[0069] The longest axial length of a thermoplastic binder particle of the elongate reinforcing structure can be determined by measuring the largest dimension across the binder particle adhered to the pultruded plank. An optical microscope such as a Keyence™ optical microscope may be used to determine the longest axial length of a binder particle adhered to the pultruded plank. The binder particle size distribution can be determined using an optical microscope (such as a Keyence™ optical microscope, e.g., Keyence™ VHX-500) and associated image analysis software (for example, ImageJ software). The binder particle size distribution can be determined using an optical microscope and associated image analysis software (for example, as described herein) to calculate the binder particle size distribution over a given area of elongate reinforcing structure (for example, an area of elongate reinforcing structure in the range of about 5 mm2to about 50 mm2, for example an area of elongate reinforcing structure in the range of about 5 mm2to about 20 mm2, an area of elongate reinforcing structure in the range of about 5 mm2to about 10 mm2). In Examples, the binder particle size distribution can be determined using an optical microscope and associated image analysis software (for example, as described herein) to calculate the binder particle size distribution over a 5mm2or 10mm2area of elongate reinforcing structure.

[0070] In embodiments, the thermoplastic binder of the elongate reinforcing structure can be described as thermoplastic binder particles having a volume average particle size (i.e. after application and adherence / fixing (e.g. by melting) to the pultruded plank) may be determined using a numerical aperture microscope (for example Keyence™ VHX-500) and associated image analysis software (for example, the size of each particle may be determined as the largest dimension across the particle, i.e. the longest axial length of the particle adhered to the surface of the pultruded plank). In embodiments, the volume average particle size of the thermoplastic binder particles after application and adherence / fixing to the pultruded plank is in the range of about 10 pm to about 1mm, for example about 20 pm to about 600 pm, about 30 pm to about 500 pm.

[0071] In embodiments, the thermoplastic binder of the elongate reinforcing structure can be described as thermoplastic binder particles and the thermoplastic binder particles before being applied to the pultruded plank have a D90 particle size of less than (i.e. 90% by volume of the particles have a particle size less than) about 1 mm, for example less than about 800 pm, less than about 600 pm, less than about 500 pm, less than about 400 pm, less than about 300 pm, or less than about 200 pm. The D90 particle size (by volume) may be determined by sieve analysis according to ISO 8130- 1.

[0072] Process for producing an elongate reinforcing structure for a wind turbine blade

[0073] Also described herein is a method for producing elongate reinforcing structure for a wind turbine blade, the method comprising: drawing glass reinforcing fibers and a thermosetting resin through a pultrusion die to form a pultruded plank at a pultrusion die outlet; applying thermoplastic binder particles to a surface of the pultruded plank; and adhering the thermoplastic binder particles to the surface of the pultruded plank.

[0074] A conventional pultrusion process and apparatus may be used to provide the pultruded plank onto which the thermoplastic binder is applied.

[0075] In embodiments, the step of applying the thermoplastic binder to a surface of the pultruded plank is carried out after the reinforcing fibers and thermosetting resin are extruded from the pultrusion die as a pultruded plank. Conventionally, a pultruded plank has a temperature of at least about 200 °C when it is extruded from the exit of a pultrusion die.

[0076] In embodiments, the process comprises applying the thermoplastic binder to a surface of the pultruded plank after the pultruded plank exits the die before the temperature of the pultruded plank cools below the glass transition temperature of the thermoplastic binder such that the thermoplastic binder adheres to the surface of the pultruded plank.

[0077] In embodiments, the process comprises applying the thermoplastic binder to a surface of the pultruded plank and heating the thermoplastic binder to a temperature of at least the glass transition temperature of the thermoplastic binder such that the thermoplastic binder adheres to the surface of the pultruded plank.

[0078] In embodiments, the process comprises applying the thermoplastic binder to a surface of the pultruded plank after the pultruded plank exits the die before the temperature of the pultruded plank cools below the melting temperature of the thermoplastic binder such that the thermoplastic binder melts on the surface of the pultruded plank and adheres to the surface of the pultruded plank as the pultruded plank cools.

[0079] In embodiments, adhering the thermoplastic binder to the pultruded plank comprises cooling the elongate reinforcing structure such that the thermoplastic binder solidifies.

[0080] In embodiments, the process comprises cooling the pultruded plank exiting the pultrusion die to a temperature of less than about 250 °C, for example less than about 250 °C, less than about 200 °C, less than about 150 °C, or less than about 120 °C, before applying the thermoplastic binder to a surface of the pultruded plank.

[0081] In embodiments, the process comprises applying the thermoplastic binder to the pultruded plank following exit from the pultrusion die when the pultruded plank has a temperature of at least about 60°C, for example at least about 70°C, at least about 80°C, at least about 100°C, or at least about 120°C.

[0082] In embodiments, the process comprises applying the thermoplastic binder to the pultruded plank when the pultruded plank reaches a temperature in the range of about 60°C to about 250 °C, for example about 60°C to about 200 °C, about 70°C to about 150 °C, or about 70°C to about 120 °C, following exit from the pultrusion die.

[0083] Structural Component Also described herein is a structural component, for example a structural component of a wind turbine blade, comprising an elongate reinforcing structure as described herein.

[0084] A structural component may comprise a plurality of elongate reinforcing structures described herein.

[0085] In embodiments, the structural component may be impregnated with a resin and the resin cured to form a composite article.

[0086] Examples

[0087] The following illustrates examples of the elongate reinforcing structures for a wind turbine blade and related aspects described herein. Thus, these examples should not be considered to restrict the present disclosure, but are merely in place to teach how to carry out the processes and obtain the products of the present disclosure.

[0088] A pultruded plank was provided by drawing continuous glass fibers and thermosetting resin through a pultrusion die. As the pultruded plank exited the die, a powder of thermoplastic binder was applied to the pultruded plank in an amount of about 10 g / m2to provide a homogeneous distribution of thermoplastic binder particles on a surface of the pultruded plank. At the point at which the thermoplastic binder was applied to the pultruded plank, the temperature of the pultruded plank was about 200 °C. As the thermoplastic binder contacted the heated pultruded plank, the thermoplastic binder melted, as the pultruded plank cooled the thermoplastic binder adhered to the pultruded plank to form an elongate reinforcing structure as shown in Figure 2. The thermoplastic binder formed discrete binder particles on the surface of the pultruded plank.

[0089] The present inventors found that the elongate reinforcing structure provided in the Example above had a textured surface formed by the thermoplastic binder particles adhered to the surface of the pultruded plank. Therefore, the elongate reinforcing structure was found to be suitable to produce a structural component such as a wind turbine blade without requiring the addition of a peel-ply layer.

[0090] The inventors consider that the discrete binder particles formed by the thermoplastic binder particles adhering to the surface of the pultruded plank allows for the elongate reinforcing structures described herein to aid resin infusion between stacked pultruded planks which avoids the use of a peel-ply layer, which in turn improves the efficiency of providing a structural component and avoids the waste caused by the use of peel-ply layers. The elongate reinforcing structures produced according to the Example were found to handle extremely well, without shedding binder.

[0091] The binder applied to the pultruded plank in this example was a polyester based thermoplastic binder. The polyester-based thermoplastic binder particles were obtained from Coim™ and had a glass transition temperature of 46 °C (determined using DSC as described above), and a softening point of 57 °C which was determined using an oscillatory rheometer in accordance with the method described above, a volume average particle size of about 185 pm determined using a dynamic light scattering technique by employing a Particle Size Analyzer (LS13320 from Beckman™), see also figure 1, line A), a shear modulus, G, at 30 °C of 30.7 MPa (determined using an oscillatory rheometer as set out above), a dynamic viscosity, q, at 130 °C of 387 Pa.s (determined using an oscillatory rheometer as set out above), a molecular weight, Mw, of 185710 and a polydispersity of 28.87 (determined as Mw / Mn)).

[0092] Other thermoplastic binders can be used. Figure 1 shows a graph showing examples of the particle size distribution of different thermoplastic powder binder particles that may be used to provide an elongate reinforcing structure as described herein.

[0093] Measurement methods

[0094] The glass transition temperature of the binder was determined using differential scanning calorimetry (DSC) according to EN ISO 11357-2 (determination of glass transition temperature) heating the binder under an air flow of 80 mL / min at a heating rate of lOK / min, heating from - 60 °C to 120 °C and then holding for 5 mins at 120 °C before cooling from 120 °C to - 60 °C at a cooling rate of lOK / min and then holding for 5 mins at - 60 °C before heating from - 60 °C to 120 °C again at a heating rate of lOK / min. The glass transition temperature was determined as the value provided on the second heating cycle.

[0095] The volume average particle size of the binder that was applied to the pultruded planks described in the Example to provide elongate reinforcing structures were determined using a dynamic light scattering technique on a dispersion of the binder using a Particle size analyzer (LS13320 Particle Size Analyzer from Beckman™) and using a dynamic light scattering technique on a dispersion of the binder in accordance with ISO 13320 2009 norm.

[0096] The shear modulus, G, at 30 °C of the binder employed in the Example was determined using a oscillatory rheometer at 0.1% deformation in plan-plan geometry, a frequency of 1 Hz with a binder sample having a thickness of 400 pm and diameter of 25 mm, employing a heating-cooling-heating cycle which heats from 30°C-130°C at a heating rate of 3°C / min, cooling from 130°C-30°C and heating from 30°C-130°C at a heating rate of 3°C / min.

[0097] The dynamic viscosity, q, at 130 °C of the binder employed in the Example was determined using a oscillatory rheometer at 0.1% deformation in plan-plan geometry, a frequency of 1 Hz with a binder sample having a thickness of 400 pm and diameter of 25 mm, employing a heating-cooling-heating cycle which heats from 30°C-130°C at a heating rate of 3°C / min, cooling from 130°C-30°C and heating from 30°C-130°C at a heating rate of 3°C / min.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0102] If a standard test is mentioned herein, unless otherwise stated, the version of the test to be referred to is the most recent at the time of filing this patent application.

[0103] 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.

[0104] 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%.

Claims

Claims:

1. An elongate reinforcing structure for a wind turbine blade, the elongate reinforcing structure comprising: a pultruded plank comprising glass reinforcing fibers and a thermoset resin, the pultruded plank having a surface; and thermoplastic binder particles adhered to the surface of the pultruded plank.

2. An elongate reinforcing structure according to claim 1 comprising a homogenous distribution of thermoplastic binder particles adhered to a surface of the pultruded plank in an amount of at least about 5 g / m2of the thermoplastic binder particles.

3. An elongate reinforcing structure according to any of the preceding claims comprising from about 5 g / m2to about 100 g / m2of the thermoplastic binder particles.

4. An elongate reinforcing structure according to any of the preceding claims, wherein the thermoplastic binder has a glass transition temperature of up to about 220 °C, optionally wherein the thermoplastic binder has a glass transition temperature in the range of about 40 °C to about 150 °C.

5. An elongate reinforcing structure according to any of the preceding claims, wherein the thermoplastic binder comprises epoxy, acrylate, or ester functional groups.

6. An elongate reinforcing structure according to any of the preceding claims, wherein the reinforcing fibers constitute from about 55 wt.% to about 95 wt.% by total weight of the pultruded plank, and the resin constitutes from about 5 wt.% to about 45 wt.% of the pultruded plank.

7. An elongate reinforcing structure according to any of the preceding claims, wherein the thermoplastic binder particles adhered to the pultruded plank have a longest axial length of less than about 1 mm.

8. A wind turbine blade comprising an elongate reinforcing structure of any of the preceding claims.

9. A process for producing an elongate reinforcing structure for a wind turbine blade, the process comprising: drawing glass reinforcing fibers and a thermosetting resin through a pultrusion die to form a pultruded plank at a pultrusion die outlet; applying thermoplastic binder particles to a surface of the pultruded plank,; and adhering the thermoplastic binder particles to the surface of the pultruded plank.

10. A process according to claim 9, wherein the thermoplastic binder having a glass transition temperature of up to about 220 °C, optionally wherein the process comprises applying the thermoplastic binder to the pultruded plank when the pultruded plank reaches a temperature in the range of about 60°C to about 250 °C following exit from the pultrusion die.

11. A process according to claim 9 or claim 10, wherein adhering the thermoplastic binder particles to the surface of the pultruded plank comprise heating the thermoplastic binder particles to a temperature of at least the glass transition temperature of the thermoplastic binder on the surface of the pultruded plank, and cooling the thermoplastic binder particles such that the thermoplastic binder particles adhere to the surface of the pultruded plank.

12. A process according to any of claims 9 to 11, wherein the thermoplastic binder particles are applied to pultruded plank in an amount in the range of about 5 g / m2to about 100 g / m2to provide a homogeneous distribution of thermoplastic binder particles on the surface of the pultruded plank.

13. A process according to any of claims 9 to 12, wherein the thermoplastic binder particles are applied and adhered to the pultruded plank, such that the thermoplastic binder particles adhered to the pultruded plank have a longest axial length of less than about 1 mm.

14. A process according to any of claims 9 to 13, wherein the wherein the reinforcing fibers constitute from about 55 wt.% to about 95 wt.% by total weight of the pultruded plank, and the resin constitutes from about 5 wt.% to about 45 wt.% of the pultruded plank.

15. An elongate reinforcing structure for a wind turbine blade obtainable by the process of any of claims 10 to 14.

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