Polyurethane-based spar cap for wind turbine blade and method of making same

Abstract

The invention relates to a preparation method of a spar cap of a wind turbine blade. The preparation method comprises the following steps: a) preparing a polyurethane-based pultrusion strip by adopting a pultrusion method; b) stacking a plurality of polyurethane-based pultruded strips in a vacuum infusion mold; c) bonding the polyurethane-based pultruded strip and the resin through vacuum infusion; and d) curing the injected resin. Also provided is a spar cap of a wind turbine blade, comprising: i) a plurality of polyurethane-based pultruded strips; and ii) a resin that bonds the polyurethane-based pultruded strip.

Description

Technical Field

[0001] The present invention relates to a spar cap for a wind turbine blade and a method for preparing the spar cap. Background Art

[0002] Wind energy is one of the clean energy sources that helps reduce greenhouse gas emissions. As one of the main components of wind turbines, wind turbine blades are aerodynamically designed and their lengths are becoming longer and longer in order to capture more wind energy. Modern wind turbine blades include one or more longitudinally extending spars that serve as load-bearing structures. The spars usually include spar caps and shear webs connected between the spar caps.

[0003] As one of the structural elements of wind turbine blades, the spar cap contains a number of pultruded strips, which are usually unidirectionally reinforced with glass fiber, carbon fiber or a combination thereof, depending on the blade design. To form the spar cap, these pultruded strips are bonded by resins including epoxy resin and polyurethane, for example by vacuum infusion.

[0004] Pultruded tapes are currently made using a matrix resin (usually epoxy) through a pultrusion process. However, the slow curing speed of epoxy resins limits their production capacity and cannot meet the rapidly growing industry needs. In addition, the low tensile strength of epoxy resins results in low transverse tensile strength of epoxy-based pultruded tapes, which limits the full utilization of the reinforcement properties.

[0005] In addition, the surface of pultruded tapes made of epoxy resin is smooth like glass, which poses a challenge to bonding. Therefore, in the pultrusion process, it is necessary to lay a peel layer on the epoxy resin-based pultruded tape and remove the peel layer before stacking the pultruded tapes to provide a rough surface that is conducive to bonding. However, the peel layer brings processing challenges such as cracking in the pultrusion die, damage to the fiber when removed, and increased cost.

[0006] WO2018 / 206068A1 discloses a pultrusion method for manufacturing a pultruded strip suitable for forming a spar cap of a wind turbine blade, the method comprising: dragging a resin-coated reinforcing fiber through a pultrusion die along a process direction to form a core of the strip; and applying another resin to one or more surfaces of the core to form a sacrificial resin layer defining the adherend surface of the strip. The pultrusion method also includes: removing resin from the sacrificial layer to activate the adherend surface, for example, by abrasion, sandblasting, and high-energy surface treatment to obtain a rough surface. It is believed that removing the sacrificial layer will increase the production cost of the spar cap and may damage the core of the pultruded strip.

[0007] CN114248474A discloses a method for preparing a polyurethane pultruded composite material, wherein a peeling layer is provided on the outer surface of the composite material to improve the surface roughness. The disclosed method comprises the following steps: 1) covering at least a portion of at least one fiber-reinforced material with at least one peeling layer; 2) impregnating the fiber-reinforced material with a polyurethane composition; 3) pulling the impregnated fiber-reinforced material and the peeling layer through a mold, and obtaining the polyurethane pultruded composite material after curing and molding. Before further processing and using the obtained polyurethane pultruded composite material, the peeling layer is removed to obtain a polyurethane pultruded composite material with the required rough surface.

[0008] WO2019 / 072948A1 discloses a composite wind turbine blade, the blade comprising a blade shell, a web, a spar cap and a blade root, characterized in that the spar cap is made of polyurethane resin by vacuum infusion or prepreg method, and the blade shell is made of epoxy resin. In this application, the spar cap is not made of pultruded strips.

[0009] Therefore, there is a need to develop a spar cap for a wind turbine blade having high tensile strength and good bonding strength with a bonding resin applied between pultruded strips without requiring surface activation of the pultruded strips, such as applying a release ply. Summary of the invention

[0010] To this end, the present invention provides a method for preparing a spar cap of a wind turbine blade, comprising the following steps:

[0011] a) preparing a polyurethane (PU) based pultruded strip by a pultrusion method;

[0012] b) stacking a plurality of polyurethane-based pultruded strips in a vacuum infusion mold;

[0013] c) bonding the polyurethane based pultruded strips with resin by vacuum infusion; and

[0014] d) Curing the injected resin.

[0015] The present invention also provides a spar cap for a wind turbine blade, comprising:

[0016] i) a plurality of polyurethane-based pultruded strips; and

[0017] ii) Resins for bonding polyurethane based pultruded tapes.

[0018] The spar caps for wind turbine blades were found to have high tensile strength and good bonding strength with the bonding resin applied between the pultruded strips without the need for surface activation of the pultruded strips, such as application of a release ply. DETAILED DESCRIPTION

[0019] The present invention is described in detail below. It should be understood that the present invention can be implemented in many different ways and should not be construed as being limited to the embodiments set forth herein.

[0020] Unless otherwise specified, all technical and scientific terms used herein have the meaning commonly understood by one of ordinary skill in the art to which the invention belongs. Unless otherwise specified, the following terms used herein have the meanings ascribed to them below.

[0021] As used herein, the articles "a" and "an" refer to one or to more than one (ie, to at least one) of the grammatical object of an item or component.

[0022] As used herein, the terms "comprising" and "including" and the like are used interchangeably and should be interpreted in a non-restrictive, open manner. That is, for example, additional components or elements may be present. The expression "consisting of" or "consisting essentially of" or cognates may be included within "comprising" or cognates.

[0023] Unless otherwise indicated, all percentages (%) are by weight.

[0024] Unless otherwise indicated, molecular weights of components or polymers are number average molecular weights (Mn).

[0025] In the present invention, the molecular weight of each component is measured by gel permeation chromatography (GPC) according to GB / T 21863-2008.

[0026] In the present invention, the OH value of each polyol component is determined according to DIN 53240.

[0027] In the present invention, the isocyanate index of the polyurethane is defined as the ratio of the total number of isocyanate groups of the isocyanate component used in the reaction to the total number of isocyanate-reactive groups, i.e., the number of active hydrogens in the compound having at least two isocyanate-reactive hydrogen-containing groups and the chain extender, expressed as a percentage. An isocyanate index of 100 means that for each isocyanate group of the isocyanate component, there is one active hydrogen atom, i.e., one functional group reactive toward isocyanate, in the compound having at least two isocyanate-reactive hydrogen-containing groups and the chain extender. An isocyanate index above 100 means that there are more isocyanate groups than isocyanate-reactive groups, such as hydroxyl groups.

[0028] According to the present invention, a method for preparing a spar cap for a wind turbine blade comprises the following steps:

[0029] a) preparing a polyurethane-based pultruded strip by a pultrusion method;

[0030] b) stacking a plurality of polyurethane-based pultruded strips in a vacuum infusion mold;

[0031] c) bonding the polyurethane based pultruded strips with resin by vacuum infusion; and

[0032] d) Curing the injected resin.

[0033] The spar cap of a wind turbine blade prepared according to the method of the present invention comprises:

[0034] i) a plurality of polyurethane-based pultruded strips; and

[0035] ii) Resins for bonding polyurethane based pultruded tapes.

[0036] In one embodiment of the present invention, the polyurethane-based pultruded strip comprises a reinforcement material.

[0037] In one embodiment of the present invention, the polyurethane-based pultruded tape may contain 70 to 95 wt %, preferably 80 to 90 wt %, for example 82 to 86 wt % of reinforcing material, based on the total weight of the polyurethane-based pultruded tape.

[0038] In one embodiment of the present invention, the polyurethane-based pultruded tape may contain 5 to 30 wt %, preferably 10 to 20 wt %, for example 14 to 18 wt % of polyurethane, based on the total weight of the polyurethane-based pultruded tape.

[0039] In one embodiment of the present invention, the resin bonding the polyurethane-based pultruded tape comprises epoxy resin, polyurethane resin or a combination thereof.

[0040] In one embodiment of the present invention, no peel ply or sacrificial layer is applied to the polyurethane-based pultruded strip. This avoids the situation where damaged peel ply fibers are left on the spar cap strip due to the absence of a peel ply or sacrificial layer, and simplifies the production process. In addition, the elimination of the peel ply or sacrificial layer saves the required volume of resin that would otherwise be absorbed by or coated on the layer and would need to be disposed of.

[0041] In one embodiment of the present invention, a layer of glass fiber cloth is placed between two adjacent polyurethane-based pultruded strips. The glass fiber cloth placed between the pultruded strips forms a flow channel for the vacuum infusion resin and prevents or reduces the space between the pultruded strips where the resin cannot enter. Therefore, the stacked pultruded strips and the glass fiber cloth placed therebetween form a complete spar cap after curing.

[0042] According to the present invention, the polyurethane-based pultruded tape has a 0° tensile strength of 1500-1800 MPa, such as 1600 MPa, 1700 MPa, etc., which is measured according to ISO527-5.

[0043] According to the present invention, the polyurethane-based pultruded tape has a 0° tensile modulus of 60-80 GPa, such as 65 GPa, 70 GPa, 75 GPa, etc., which is measured according to ISO527-5.

[0044] According to the present invention, the polyurethane-based pultruded tape has a transverse tensile strength (90° tensile strength) of 55-85 MPa, preferably 60-80 MPa, such as 65 MPa, 70 MPa, 75 MPa, etc., which is measured according to ISO527-5.

[0045] According to the present invention, the polyurethane-based pultruded tape has a transverse tensile modulus (90° tensile modulus) of 15-25 GPa, for example, 16 GPa, 17 GPa, 18 GPa, 19 GPa, 20 GPa, 21 GPa, 22 GPa, 23 GPa, 24 GPa, etc., which is measured according to ISO527-5.

[0046] According to the present invention, the polyurethane-based pultruded tape has a 0° compressive strength of 1400-1800 MPa, such as 1500 MPa, 1600 MPa, 1700 MPa, etc., which is measured according to ISO14126.

[0047] According to the present invention, the polyurethane-based pultruded tape has a 0° compression modulus of 60-80 GPa, such as 65 GPa, 70 GPa, 75 GPa, etc., measured according to ISO14126.

[0048] According to the present invention, the polyurethane-based pultruded strip has a transverse compressive strength (90° compressive strength) of 160-200 MPa, for example 165 MPa, 170 MPa, 175 MPa, 180 MPa, 185 MPa, 190 MPa, 195 MPa, etc., which is measured according to ISO14126.

[0049] According to the present invention, the polyurethane-based pultruded tape has a transverse compression modulus (90° compression modulus) of 21-25 GPa, such as 22 GPa, 23 GPa, 24 GPa, etc., which is measured according to ISO14126.

[0050] According to the present invention, the polyurethane-based pultruded tape has a single lap shear strength of 25-45 MPa, preferably 26-40 MPa, such as 27 MPa, 28 MPa, 29 MPa, 30 MPa, 32 MPa, 35 MPa, 40 MPa, etc., which is determined according to DIN 1465.

[0051] According to the present invention, the polyurethane-based pultruded tape has a tension-tension fatigue (R=0.1) of 8-10, which is measured according to ISO13003.

[0052] According to the present invention, the polyurethane-based pultruded strip is made of polyurethane and a reinforcing material by a pultrusion molding method.

[0053] As is well known in the art, the pultrusion process is a continuous process for producing fiber-reinforced profiles with a constant cross section. A pultrusion device usually consists of an impregnation unit and a heated die head as well as a take-up system responsible for the continuity of the process. The impregnation of the fibers takes place in an open bath or in a closed injection box. Here the reinforcing material, such as glass fiber or carbon fiber, is wetted with resin. The composite is then formed and hardened in a heated die head. The take-up system removes the finished profile from the die head and finally cuts it to the desired length.

[0054] In one embodiment of the present invention, the pultrusion process is carried out at a temperature of 100°C to 220°C, such as 120°C, 140°C, 160°C, 180°C, 200°C, etc.

[0055] In one embodiment of the invention, the polyurethane-based pultruded strip has a thickness in the range of 1 mm to 15 mm, such as 5 mm to 10 mm, and has a width in the range of 5 cm to 35 cm, such as 10 cm to 20 cm.

[0056] In one embodiment of the present invention, the polyurethane-based pultruded tape has no release layer or sacrificial layer.

[0057] In one embodiment of the invention, the spar cap has 2 to 10 polyurethane based pultruded strips, such as 3, 4, 5, 6, 7, 8, 9 polyurethane based pultruded strips.

[0058] Polyurethane

[0059] In one embodiment of the present invention, the polyurethanes herein are obtainable by reacting a compound having at least two isocyanate-reactive hydrogen atoms with an isocyanate, such as a diisocyanate and / or a polyisocyanate, optionally in the presence of a catalyst.

[0060] In a preferred embodiment of the present invention, the polyurethane is obtained by reacting a polyol with an isocyanate, such as a diisocyanate and / or a polyisocyanate, optionally in the presence of a catalyst.

[0061] As is well known in the art, polyurethanes cure faster than epoxies.

[0062] Polyols

[0063] In the present invention, the component for forming the polyurethane may include a polyol. The polyol may have a number average molecular weight (Mn) of 160 to 5000 g / mol, preferably 240 to 4800 g / mol, more preferably 260 to 4200 g / mol.

[0064] The polyol may be a polyol commonly used in the preparation of polyurethane, such as polyether polyol, polyester polyol such as polycaprolactone polyol, polycarbonate polyol, and combinations thereof, preferably polyether polyol.

[0065] The polyol in the present invention can be prepared by methods known in the art or can be commercially obtained.

[0066] In one embodiment of the invention, the polyol may be selected from polyether polyols derived from oxygen-containing heterocyclic compounds containing 2 to 6 carbon atoms, such as 3, 4, 5 or 6 carbon atoms, preferably alkyl oxiranes. Preferably, the polyol is prepared by polymerizing oxiranes and methyloxiranes as repeating units, preferably terminated with secondary hydroxyl groups.

[0067] In a preferred embodiment of the present invention, the polyol is selected from polyether polyols derived from epoxides, preferably ethylene oxide, propylene oxide or mixtures thereof.

[0068] In one embodiment of the invention, the polyol may be selected from polyester polyols, including, for example, polyester polyols obtained from dicarboxylic acids and polyols having 2 to 12 carbon atoms, preferably 4 to 6 carbon atoms. Suitable dicarboxylic acids include, but are not limited to, aliphatic dicarboxylic acids, such as succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid and sebacic acid; or aromatic dicarboxylic acids, such as phthalic acid, isophthalic acid and terephthalic acid. The dicarboxylic acids may be used alone or as a mixture, for example, as a mixture of succinic acid, glutaric acid and adipic acid. In order to prepare polyester polyols, corresponding dicarboxylic acid derivatives, such as carboxylic acid diesters, anhydrides or acid chlorides having 1 to 4 carbon atoms in the alcohol residue may optionally be used instead of dicarboxylic acids. Examples of suitable polyols include glycols having 2 to 10 carbon atoms, preferably 2 to 6 carbon atoms, such as ethylene glycol, diethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,10-hexanediol, 2,2-dimethyl-1,3-propanediol, 1,3-propanediol or dipropylene glycol. Depending on the desired properties, the polyester polyols can be used alone or as a mixture. Preferred polyester polyols include poly(ethylene glycol adipate), poly(1,4-butanediol adipate), poly(ethylene glycol / 1,4-butanediol adipate), poly(1,6-hexanediol / neopentyl glycol adipate), poly(1,6-hexanediol / 1,4-butanediol adipate) and polycaprolactone, ω-hydroxycarboxylic acid, for example, condensation products of ω-hydroxycaproic acid or lactones, for example, polymerization products of optionally substituted ω-caprolactone.

[0069] In one embodiment of the present invention, the polyol may be selected from polycarbonate polyols derived from carbonic acid and diols, especially diols having 4 to 6 carbon atoms, such as 1,4-butanediol or 1,6-hexanediol.

[0070] The polyol is preferably used in an amount of 45 to 80 wt %, such as 45, 50, 55, 60, 65, 70, 75, 80, etc., based on the total weight of the polyurethane.

[0071] Isocyanate

[0072] In the present invention, the component for forming polyurethane may include isocyanate. The isocyanate may include all isocyanates known for producing polyurethane. These isocyanates include aliphatic, alicyclic, aromatic aliphatic and / or aromatic isocyanates, such as tri-, tetra-, penta-, hexa-, hepta- and / or octamethylene diisocyanate, 2-methylpentamethylene 1,5-diisocyanate, 2-ethylbutylene 1,4-diisocyanate, pentamethylene 1,5-diisocyanate, butylene 1,4-diisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate, IPDI), 1,4- and / or 1,3-bis(isocyanatomethyl)cyclohexane (HXDI), cyclohexane 1,4- diisocyanates, 1-methylcyclohexane 2,4- and / or 2,6-diisocyanate and / or dicyclohexylmethane 4,4'-, 2,4'- and 2,2'-diisocyanate, diphenylmethane diisocyanate (MDI), including diphenylmethane 2,2'-, 2,4'- and / or 4,4'-diisocyanate, polymeric MDI, naphthalene 1,5-diisocyanate (NDI), toluene 2,4- and / or 2,6-diisocyanate (TDI), 3,3'-dimethyldiphenyl diisocyanate, 1,2-diphenylethane diisocyanate and / or phenylene diisocyanate, or mixtures thereof.

[0073] Preferably, the isocyanate comprises MDI, particularly 4,4'-diphenylmethane diisocyanate.

[0074] The isocyanate is preferably used in an amount of 15 to 50 wt %, such as 15, 20, 25, 30, 35, 40, 45, 50, etc., based on the total weight of the polyurethane.

[0075] Chain Extender

[0076] In the present invention, the components for forming the polyurethane may include a chain extender.

[0077] Chain extenders which can be used are substances having a molecular weight of preferably less than 500 g / mol, particularly preferably in the range of 60 to 400 g / mol, wherein the chain extenders have 2 or more, for example 3, hydrogen atoms which are reactive toward isocyanates. These chain extenders can be used alone or in the form of a mixture. Preference is given to using diols having a molecular weight of less than 500 g / mol, in particular 60 to 400 g / mol, and very particularly 60 to 350 g / mol. Examples which can be used are aliphatic, cycloaliphatic and / or araliphatic diols having 2 to 14, preferably 2 to 10, carbon atoms, for example ethylene glycol, 1,3-propylene glycol, 1,4-butanediol (1,4-BDO), 1,6-hexanediol, 1,10-decanediol, 1,2-, 1,3- and 1,4-dihydroxycyclohexane, diethylene glycol, dipropylene glycol, tripropylene glycol, diethanolamine. Preference is given to using ethylene glycol, 1,3-propylene glycol or 1,4-butanediol, especially 1,4-butanediol.

[0078] The amount of chain extender used is preferably 1 wt % to 11 wt %, more preferably 3 wt % to 8 wt %, for example 1 wt %, 2 wt %, 3 wt %, 4 wt %, 5 wt %, 6 wt %, 7 wt %, 8 wt %, 9 wt %, 10 wt %, 11 wt %, based on the total weight of the polyurethane.

[0079] catalyst

[0080] In the present invention, the components for forming the polyurethane may optionally contain a catalyst.

[0081] As the catalyst, all compounds capable of accelerating the reaction between isocyanate and polyol can be used. These catalysts include amine-based catalysts and organometallic compound-based catalysts, or mixtures thereof.

[0082] As the amine-based catalyst, for example, a strongly basic amine such as N,N,N-triethylaminoethoxyethanol, bis(N,N-dimethylaminoethyl) ether, dimethylcyclohexylamine, trimethylhydroxyethylethylenediamine, dimethylbenzylamine, triethylamine, triethylenediamine, pentamethyldipropylenetriamine, dimethylethanolamine, N-methylimidazole, N-ethylimidazole, tetramethylhexamethylenediamine, tris(dimethylaminopropyl)hexahydrotriazine, dimethylaminopropylamine, N-ethylmorpholine, diazabicycloundecene, diazabicyclononene, diazabicyclooctane can be used, preferably triethylenediamine or bis(N,N-dimethylaminoethyl) ether.

[0083] As the catalyst based on an organometallic compound, for example, an organotin compound such as tin(II) salts of organic carboxylic acids, such as tin(II) acetate, tin(II) octoate, tin(II) ethylhexanoate and tin(II) laurate, and dialkyltin(IV) salts of organic carboxylic acids, such as dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate and dioctyltin diacetate, and a Zn salt or a Bi salt, such as zinc octoate, bismuth(III) neodecanoate, bismuth 2-ethylhexanoate and bismuth octoate, or an alkali metal salt of a carboxylic acid, such as potassium acetate or potassium formate, can be used.

[0084] If used, the catalyst is preferably used in an amount of 0.1 ppm to 500 ppm, more preferably 1 ppm to 100 ppm, based on the total weight of the polyurethane.

[0085] According to the present invention, the isocyanate index of the polyurethane is in the range of 95 to 120, such as 105, 115, etc., preferably in the range of 100 to 110, such as 105.

[0086] In the present invention, the polyurethane optionally contains additives.

[0087] Additives that can be used in the present invention include, but are not limited to, chain regulators, lubricants, surfactants, preservatives, pigments or dyes, toughening agents or impact modifiers, antistatic agents, defoamers, leveling agents, plasticizers, flame retardants, film formers, antioxidants, waxes, UV-resistant additives, stabilizers, thickeners, wetting agents, fillers, or mixtures thereof. When preparing polyurethane, preferably one of the above additives or a mixture thereof is used.

[0088] If present, such additives are generally used in amounts of 0.1 to 10 wt % based on the total weight of the polyurethane.

[0089] As for the chain regulator, it includes an alkyl alcohol having one hydroxyl group, for example, the number of carbon atoms of the alkyl alcohol can be 2-30, preferably 4-26, more preferably 10-22. Preferably, an alkyl alcohol having one hydroxyl terminal group having 10-20 carbon atoms, preferably 14-18 carbon atoms, is preferred, and 1-tetradecanol is particularly preferred. If present, the amount of the chain regulator is preferably 0.1 wt % to 1.0 wt %, such as 0.2 wt %, 0.3 wt %, 0.4 wt %, 0.5 wt %, 0.6 wt %, 0.7 wt %, 0.8 wt %, 0.9 wt %, etc., based on the total weight of the polyurethane.

[0090] As antioxidants, all compounds customarily used for the preparation of polyurethanes may be used, for example tea polyphenols (TP), tocopherols, flavonoids, butylhydroxyanisole (BHA), butylhydroxytoluene (BHT), tert-butylhydroquinone (TBHQ), etc. If present, the amount of the antioxidant is preferably from 0.1% to 1.5% by weight, for example 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.2%, 1.3%, 1.4%, etc., based on the total weight of the polyurethane.

[0091] As lubricants, all compounds customary for the preparation of polyurethanes may be used, for example alkoxylated fatty acid esters, alkoxylated fatty alcohols, fatty amine salts, etc. If present, the amount of lubricant is preferably from 0.1 to 1.0% by weight, for example 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, etc., based on the total weight of the polyurethane.

[0092] As anti-UV additives, all compounds suitable for preparing polyurethanes can be used, such as salicylates, phenyl ketones, benzotriazoles, substituted acrylonitriles, triazines, etc. If present, the amount of the anti-UV additive is preferably 0.1% to 1.0% by weight, such as 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, based on the total weight of the polyurethane.

[0093] For pigment or dye, all compounds suitable for preparing polyurethane can be used, such as carbon black, aniline black, titanium dioxide, red iron oxide, titanium yellow, isoindolinone pigment, cadmium oxide, phthalocyanine green, chrome red, acridazine, anthraquinone, acridine, anthocyanin, oxazine, thiazine, etc. Preferably, the pigment or dye can be used in the form of a color paste. If present, the amount of the pigment or dye is preferably 0.1% by weight to 2.0% by weight, such as 0.2% by weight, 0.3% by weight, 0.4% by weight, 0.5% by weight, 0.6% by weight, 0.7% by weight, 0.8% by weight, 0.9% by weight, 1.0% by weight, 1.1% by weight, 1.2% by weight, 1.3% by weight, 1.4% by weight, 1.5% by weight, 1.6% by weight, 1.7% by weight, 1.8% by weight, 1.9% by weight, etc., based on the gross weight of polyurethane.

[0094] As tougheners or impact modifiers, all compounds suitable for preparing polyurethanes can be used, such as core-shell rubbers, silicate powders, powdered kaolin, etc. If present, the amount of tougheners or impact modifiers is preferably 1% to 2% by weight, such as 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, etc., based on the weight of the total polyurethane.

[0095] As fillers, all compounds suitable for preparing polyurethanes may be used, for example calcium carbonate, barium sulfate, clay, aluminum trihydrate, wollastonite, talc, mica, flake glass, silica, etc. If present, the amount of fillers is preferably from 0.1% to 1.0% by weight, for example 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, etc., based on the total weight of the polyurethane.

[0096] As film formers, all compounds suitable for preparing polyurethanes can be used, for example polyvinylamines, polyamides, etc. If present, the amount of film former is preferably 0.1% to 1.0% by weight, for example 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, etc., based on the total weight of the polyurethane.

[0097] Those skilled in the art may also select appropriate amounts of other additives.

[0098] In all embodiments described herein, the sum of the contents of the various components in the polyurethane is 100 wt %, based on the total weight of the polyurethane.

[0099] Reinforcement Materials

[0100] In the present invention, the reinforcing material can be a fiber material. The fiber material used can include any type of continuous filament fibers. Continuous filament fibers refer to a fiber material having a length of at least several meters here. The fiber material used here can include single fibers, woven fibers, fiber webs, fiber scrims and textile fibers known as fiber rovings. Preferably, the fiber material includes or is composed of glass fiber, glass net, carbon fiber, polyester fiber, natural fiber, aramid fiber, basalt fiber or nylon fiber, and particularly preferably uses glass fiber, carbon fiber or its mixture.

[0101] In a preferred embodiment of the present invention, the glass fiber is a unidirectional glass fiber.

[0102] In the present invention, the polyurethane-based pultruded tape may contain 5-30 wt % of polyurethane and 70-95 wt % of reinforcing material, based on the total weight of the polyurethane-based pultruded tape.

[0103] In a preferred embodiment of the present invention, the polyurethane-based pultruded tape may contain 10-20 wt% of polyurethane and 80-90 wt% of reinforcing material, based on the total weight of the polyurethane-based pultruded tape.

[0104] In another preferred embodiment of the present invention, the polyurethane-based pultruded tape may contain 14-18 wt% of polyurethane and 82-86 wt% of reinforcing material, based on the total weight of the polyurethane-based pultruded tape.

[0105] The present invention also provides a method for producing a polyurethane-based pultruded strip, comprising the following steps:

[0106] (1) mixing various components of the polyurethane to obtain a polyurethane reaction mixture;

[0107] (2) wetting the reinforcing material with the resulting reaction mixture; and

[0108] (3) The wetted reinforcement material is pultruded and cured.

[0109] The mixing of the components of the polyurethanes according to the invention can be carried out here in the manner customary for producing polyurethane-based reaction mixtures, for example in a high-pressure or low-pressure process.

[0110] The wetting of the reinforcing material can be carried out in an open die or preferably in a closed die. The temperature during the wetting of the reinforcing material is preferably below 100° C., preferably 0-75° C., particularly preferably 10-50° C., in particular 15-35° C., for example at room temperature.

[0111] After the wetting process, the reinforcing material wetted with the reaction mixture is preferably pulled through a die. The die can have any desired cross-sectional shape perpendicular to the pulling direction of the wet reinforcing material, but the shape is preferably as constant as possible. The temperature of the die is preferably 100-220° C., and the polyurethane reaction mixture is thus hardened to obtain a finished polyurethane.

[0112] The polyurethane-based pultruded strip is preferably pulled out of the die at a speed of more than 0.5 m / min. The take-up speed is particularly preferably more than 0.6 m / min, in particular more than 0.8 m / min, for example 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 3.0, 4.0, 5.0, etc. The resulting polyurethane-based pultruded strip is usually wound up in a take-up roll for several hundred meters.

[0113] The invention also provides a wind turbine blade comprising a spar cap according to the invention.

[0114] In one embodiment of the invention, the wind turbine blade is first manufactured as two half shells which are then bonded together with the shear web and the root portion to form the entire wind turbine blade. The method of manufacturing the half shells is well known in the art.

[0115] Implementation

[0116] Various embodiments are listed below. It should be understood that the embodiments listed below can be combined with all aspects and other embodiments within the scope of the present invention.

[0117] Embodiment 1: A method for preparing a spar cap for a wind turbine blade comprises the following steps: a) preparing a polyurethane-based pultruded strip by a pultrusion method;

[0118] b) stacking a plurality of polyurethane-based pultruded strips in a vacuum infusion mold;

[0119] c) bonding the polyurethane based pultruded strips with resin by vacuum infusion; and

[0120] d) Curing the injected resin.

[0121] Embodiment 2: The method according to embodiment 1, wherein the polyurethane-based pultruded strip comprises a reinforcement material.

[0122] Embodiment 3: The method of Embodiment 2, wherein the polyurethane-based pultruded tape comprises 5 wt% to 30 wt% polyurethane and 70 wt% to 95 wt% reinforcement material, based on the total weight of the polyurethane-based pultruded tape.

[0123] Embodiment 4: The method according to Embodiment 2 or 3, wherein the reinforcing material comprises glass fiber, carbon fiber or a combination thereof.

[0124] Embodiment 5: The method of Embodiment 4, wherein the glass fibers are unidirectional glass fibers.

[0125] Embodiment 6: The method according to any of the preceding embodiments, wherein the polyurethane is obtained by reacting a compound having at least two isocyanate-reactive hydrogen atoms with a diisocyanate and / or a polyisocyanate.

[0126] Embodiment 7: The method according to any of the preceding embodiments, wherein the resin bonding the polyurethane-based pultruded strip comprises an epoxy resin, a polyurethane resin, or a combination thereof.

[0127] Embodiment 8: The method according to any of the preceding embodiments, wherein the pultrusion process is carried out at a temperature of 100°C to 220°C.

[0128] Embodiment 9: The method according to any of the preceding embodiments, wherein no release layer or sacrificial layer is applied on the polyurethane-based pultruded tape.

[0129] Embodiment 10: The method according to any of the preceding embodiments, wherein a layer of fiberglass cloth is placed between two adjacent polyurethane-based pultruded strips.

[0130] Embodiment 11: A spar cap of a wind turbine blade, comprising:

[0131] i) a plurality of polyurethane-based pultruded strips; and

[0132] ii) Resins for bonding polyurethane based pultruded tapes.

[0133] Embodiment 12: The spar cap according to Embodiment 11, wherein the polyurethane-based pultruded strips comprise reinforcement material.

[0134] Embodiment 13: The spar cap according to Embodiment 12, wherein the polyurethane-based pultruded strip comprises 5 wt% to 30 wt% polyurethane and 70 wt% to 95 wt% reinforcement material, based on the total weight of the polyurethane-based pultruded strip.

[0135] Embodiment 14: The spar cap according to Embodiment 12 or 13, wherein the reinforcement material comprises glass fiber, carbon fiber, or a combination thereof.

[0136] Embodiment 15: The spar cap according to Embodiment 14, wherein the glass fibers are unidirectional glass fibers.

[0137] Embodiment 16: The spar cap according to any one of embodiments 11 to 15, wherein the polyurethane-based pultruded strip has a transverse tensile strength of 55-85 MPa, preferably 60-80 MPa, measured according to ISO 527-5.

[0138] Embodiment 17: The spar cap according to any one of Embodiments 11 to 16, wherein the resin bonding the polyurethane-based pultruded strips comprises an epoxy resin, a polyurethane resin, or a combination thereof.

[0139] Embodiment 18: The spar cap according to any one of Embodiments 11 to 17, wherein the polyurethane-based pultruded strip has a thickness in the range of 1 mm to 15 mm and a width in the range of 5 cm to 35 cm.

[0140] Embodiment 19: The spar cap according to any one of Embodiments 11 to 18, wherein the spar cap has 2 to 10 polyurethane-based pultruded strips.

[0141] Embodiment 20: The spar cap according to any one of embodiments 11 to 19, wherein there is a layer of fiberglass cloth between two adjacent polyurethane-based pultruded strips.

[0142] Embodiment 21: A wind turbine blade comprising a spar cap according to any one of embodiments 11 to 20 or a spar cap prepared by the method according to any one of embodiments 1 to 10.

[0143] Example

[0144] The present invention is further illustrated by examples and comparative examples, but these examples and comparative examples are not intended to limit the present invention.

[0145] The following raw materials are used:

[0146] Elastocoat CC 6226 / 100C-A&C-B are polyurethane resins from BASF.

[0147] AP3230A / B is an epoxy resin from Huibai New Materials Technology (Shanghai) Co., Ltd.

[0148] CPIC 467 is a glass fiber from Chongqing International Composite Materials Co., Ltd.

[0149] Performance Testing

[0150] The tensile strength and tensile modulus were measured according to ISO 527-5.

[0151] The compressive strength and compression modulus were measured according to ISO14126.

[0152] The single lap shear strength is determined according to DIN 1465.

[0153] Tensile-tensile fatigue R=0.1 was measured according to ISO13003.

[0154] Example 1 Preparation of polyurethane-based pultruded tapes

[0155] The pultrusion device (KraussMaffeiPUL) used here includes a closed injection box and a heatable die. The inner diameter of the flat profile in the die is 5×120 mm. Pultruded strips with these dimensions are produced accordingly. The contents of glass fibers and resins used in Example 1 of the present invention, based on the total weight of the pultruded strips, are shown in Table 1 below. The polyurethane resin is injected into the injection box, thereby wetting the glass fibers with the resin. The wetted glass fibers are continuously pulled through the die with the aid of a winding system and cured in the heated die at three zone temperatures of 100° C., 150° C. and 180° C. At the end of the process, the profile is continuously wound up.

[0156] Comparative Example 1 Preparation of epoxy resin based pultruded tapes

[0157] The pultrusion device used here includes a closed injection box and a heatable die. The inner diameter of the flat profile in the die is 5×120 mm. Pultruded strips with these dimensions are produced accordingly. The contents of glass fibers and resin used in this comparative example 1 are shown in the following Table 1, based on the total weight of the pultruded strip. Epoxy resin is injected into the injection box, thereby wetting the glass fibers with the resin. The wetted glass fibers are continuously pulled through the die by means of a take-up system and cured in the heated die at three zone temperatures of 120° C., 140° C. and 160° C. At the end of the process, the profile is continuously wound up.

[0158] Table 1

[0159] Comparative Example 1 Example 1 CPIC 467, weight % 83.5 84 AP3230A / B, weight % 16.5 Elastocoat CC 6226 / 100C-A&C-B, weight % 16

[0160] The properties of the epoxy resin-based pultruded tape (Comparative Example 1) and the polyurethane resin-based pultruded tape (Example 1) used for the spar cap are shown in Table 2 below:

[0161] Table 2

[0162]

[0163] As shown in Table 2, the polyurethane resin-based pultruded tape has better performance or at least equivalent performance relative to the epoxy resin-based pultruded tape. In particular, the 90° tensile strength and single lap shear strength of the polyurethane resin-based pultruded tape are significantly better than those of the epoxy resin-based pultruded tape.

[0164] It is obvious to those skilled in the art that various modifications and variations may be made to the present invention without departing from the scope or spirit of the present invention. These embodiments and examples are considered to be exemplary only. Therefore, the present invention is intended to cover these modifications and variations that fall within the scope of the appended claims and their equivalents.

Claims

1. A method for preparing a spar cap for a wind turbine blade, comprising the following steps: a) preparing a polyurethane-based pultruded strip by a pultrusion method; b) stacking a plurality of polyurethane-based pultruded strips in a vacuum infusion mold; c) bonding the polyurethane-based pultruded strips with resin by vacuum infusion; and d) Curing the injected resin.

2. The method of claim 1, wherein the polyurethane-based pultruded strip comprises a reinforcement material.

3. The method of claim 2, wherein the polyurethane-based pultruded tape comprises 5 to 30 weight percent polyurethane and 70 to 95 weight percent reinforcement material, based on the total weight of the polyurethane-based pultruded tape.

4. The method according to claim 2 or 3, wherein the reinforcing material comprises glass fiber, carbon fiber or a combination thereof. The method of claim 4 , wherein the glass fibers are unidirectional glass fibers.

6. The process according to any one of the preceding claims, wherein the polyurethane is obtained by reacting a compound having at least two isocyanate-reactive hydrogen atoms with a diisocyanate and / or a polyisocyanate.

7. The method according to any one of the preceding claims, wherein the resin bonding the polyurethane-based pultruded strips comprises an epoxy resin, a polyurethane resin or a combination thereof.

8. The method according to any one of the preceding claims, wherein the pultrusion process is carried out at a temperature of 100 to 220°C.

9. A method according to any one of the preceding claims, wherein no release or sacrificial layer is applied to the polyurethane based pultruded strip.

10. A method according to any one of the preceding claims, wherein a layer of glass fibre cloth is placed between two adjacent polyurethane based pultruded strips.

11. A spar cap for a wind turbine blade, comprising: i) a plurality of polyurethane-based pultruded strips; and ii) Resins for bonding polyurethane based pultruded tapes.

12. The spar cap of claim 11, wherein the polyurethane-based pultruded strips contain reinforcement material.

13. The spar cap of claim 12, wherein the polyurethane-based pultruded strip comprises 5 to 30 wt% polyurethane and 70 to 95 wt% reinforcement material, based on the total weight of the polyurethane-based pultruded strip.

14. The spar cap according to claim 12 or 13, wherein the reinforcement material comprises glass fiber, carbon fiber or a combination thereof.

15. The spar cap of claim 14, wherein the glass fibers are unidirectional glass fibers.

16. The spar cap according to any one of claims 11 to 15, wherein the polyurethane based pultruded strip has a transverse tensile strength of 55-85 MPa, preferably 60-80 MPa, measured according to ISO 527-5.

17. The spar cap according to any one of claims 11 to 16, wherein the resin bonding the polyurethane-based pultruded strips comprises epoxy resin, polyurethane resin or a combination thereof.

18. A spar cap according to any one of claims 11 to 17, wherein the polyurethane based pultruded strip has a thickness in the range of 1 mm to 15 mm and a width in the range of 5 cm to 35 cm.

19. The spar cap according to any one of claims 11 to 18, wherein the spar cap has 2 to 10 polyurethane based pultruded strips.

20. A spar cap according to any one of claims 11 to 19, wherein there is a layer of glass fibre cloth between two adjacent polyurethane based pultruded strips.

21. A wind turbine blade comprising a spar cap according to any one of claims 11 to 20 or a spar cap produced by the method of any one of claims 1 to 10.

Images