Photocurable resin composition for fiber-reinforced resin, fiber-reinforced resin composite, and method for repairing structures

Abstract

The present invention provides a photocurable resin composition for fiber-reinforced resins that combines excellent workability with high strength (particularly crack resistance) of the cured product, a fiber-reinforced resin composite containing the same, and a method for repairing structures using the same. [Solution] A photocurable resin composition used in a fiber-reinforced resin contains an epoxy compound and an oxetane compound as resin components, with the oxetane compound content being more than 30% by mass and less than 70% by mass relative to 100% by mass of the total resin components. The photocurable resin composition contains an epoxy compound, an oxetane compound, and silica as resin components, with the oxetane compound content being more than 20% by mass and less than 60% by mass relative to 100% by mass of the total resin components. A method for repairing a damaged portion D of a structure S using a photocurable resin composition involves applying a photocurable resin composition containing an epoxy compound and an oxetane compound as resin components to the surface of the damaged portion D and photocuring the composition to form a first photocured layer 1.

Description

[Technical Field]

[0001] The present disclosure relates to a photocurable resin composition for fiber-reinforced resins, a fiber-reinforced resin composite containing the same, and a method for repairing a structure using the same. [Background technology]

[0002] For example, relatively large structures such as aircraft wings and ship hulls, cement structures (buildings, etc.), their joints and piping (pipes), and wind turbine blades (hereinafter collectively referred to as "target structures") may suffer damage such as cracks and breakage caused by lightning strikes, wind erosion, bird strikes, etc. Therefore, target structures are usually required to be inspected at regular intervals, and any damage found is repaired.

[0003] Two-component epoxy resins, which have high adhesive strength and hardened strength, are generally used to repair structures. However, the use of thermosetting resins such as two-component epoxy resins has the following disadvantages. Because they require long periods of heating with a heater (for example, 10 hours or more at 70°C) to harden, finishing work must be delayed until the next day. As a result, repair work usually takes two days, which increases the maintenance cycle time. In addition, because the resin begins to thicken as soon as it is mixed, the work time (approximately 30 minutes) is limited, and speed is required for repairs. Furthermore, because the two components must be measured and mixed on-site, there is a risk of getting the ratio wrong.

[0004] Meanwhile, inspection and repair of target structures usually requires large-scale work in unstable locations using ropework, cranes, gondolas, etc. Therefore, if the work could be completed on the same day (in a one-day process) without moving, for example by using a photocurable resin that can be hardened in a short time by irradiating it with UV light, there would be great benefits in terms of reducing work time, securing the number of workers, reducing downtime, and reducing repair costs.

[0005] Furthermore, when fiber-reinforced plastic (FRP) is used in the target structure, a fiber-reinforced resin composite containing curable resin and fiber is generally used as the repair FRP. However, repair FRP requires ease of handling when and after impregnating the fibers with resin.

[0006] Under these circumstances, various UV-curable resins and fiber-reinforced resin composites containing them have been investigated (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 10-24496 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-30821 Summary of the Invention [Problem to be solved by the invention]

[0008] However, although Patent Documents 1 and 2 evaluate the complete curing after impregnation of the fibers with UV-curable resin, they do not consider the strength of the cured product obtained by curing the UV-curable resin itself. Curable resins and fiber-reinforced resins used to repair target structures are required to have high cured strength (especially crack resistance) in order to reduce damage to the repair area as well as workability.

[0009] The present disclosure has been made in consideration of the above points, and its object is to provide a photocurable resin composition for fiber-reinforced resins that combines excellent workability with high cured product strength (particularly crack resistance), a fiber-reinforced resin composite containing the same, and a method for repairing structures using the same. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to achieve the above-mentioned object and have found that in a photocurable resin composition containing an epoxy compound and an oxetane compound as resin components, specifying the content of the oxetane compound within a predetermined range not only provides excellent workability but also improves the strength of the cured product.

[0011] The first photocurable resin composition for fiber-reinforced resin of the present disclosure (hereinafter also simply referred to as "first photocurable resin composition") is a photocurable resin composition used for fiber-reinforced resin, characterized in that it contains an epoxy compound and an oxetane compound as resin components, and the content of the oxetane compound is more than 30% by mass and less than 70% by mass relative to 100% by mass of the total amount of the resin components.

[0012] A second photocurable resin composition for fiber-reinforced resins (hereinafter also simply referred to as "second photocurable resin composition") of the present disclosure is a photocurable resin composition used for fiber-reinforced resins, and is characterized in that it contains an epoxy compound, an oxetane compound, and silica as resin components, and the content of the oxetane compound is more than 20% by mass and less than 60% by mass relative to 100% by mass of the total amount of the resin components. The content of the silica may be 30% by mass or less relative to 100% by mass of the total amount of the resin components. The particle size of the silica may be 10 nm or more and 350 nm or less.

[0013] In the first photocurable resin composition and the second photocurable resin composition, the epoxy compound may include at least one selected from the group consisting of a glycidyl-type epoxy compound and an alicyclic epoxy compound.

[0014] The fiber-reinforced resin composite of the present disclosure is characterized by including a first photocurable resin composition or a second photocurable resin composition and glass fibers. The fiber-reinforced resin composite may be obtained by impregnating a sheet of the glass fibers with the first photocurable resin composition or the second photocurable resin composition.

[0015] The structure repair method disclosed herein is a method for repairing a damaged portion of a structure using a photocurable resin composition, the photocurable resin composition containing an epoxy compound and an oxetane compound as resin components, and is characterized by coating the photocurable resin composition on the surface of the damaged portion and photocuring it to form a first photocured layer. The structure repair method disclosed herein may also include coating the surface of the first photocured layer with a fiber-reinforced resin composite, obtained by impregnating a sheet of glass fiber with the photocurable resin composition using a hand layup method or a VaRTM method, and photocuring the composite to form at least one second photocured layer. The structure repair method disclosed herein may also include stacking the fiber-reinforced resin composites using a hand layup method and photocuring each layer to form multiple second photocured layer layers. The structure repair method disclosed herein may also include thermal curing after all of the second photocured layer layers have been formed. [Effects of the Invention]

[0016] According to the present disclosure, it is possible to provide a photocurable resin composition for fiber-reinforced resins that combines excellent workability with high cured product strength (particularly crack resistance), a fiber-reinforced resin composite containing the same, and a method for repairing structures using the same. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram for explaining the grinding step in the method for repairing a structure according to this embodiment. [Figure 2] FIG. 2 is a schematic diagram for explaining the pre-painting step in the method for repairing a structure according to this embodiment. [Figure 3] FIG. 3 is a schematic diagram for explaining the painting step in the method for repairing a structure according to this embodiment. [Figure 4] FIG. 4 is a schematic diagram for explaining the state of the repaired portion after the painting step in the method for repairing a structure according to this embodiment. [Figure 5] FIG. 5 is a schematic diagram for explaining the thermal curing step in the method for repairing a structure according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present embodiment will be described in detail below. The following description of the preferred embodiment is essentially merely illustrative and is not intended to limit the present invention, its applications, or its uses in any way. The following various components may be used alone or in combination of two or more. The following various components may be commercially available products or synthetic products.

[0019] <Photocurable resin composition for fiber reinforced resin> The first photocurable resin composition and the second photocurable resin composition according to this embodiment (hereinafter also collectively referred to as "photocurable resin compositions") are used for fiber-reinforced resins. In other words, the photocurable resin composition is suitably used as a matrix resin for a fiber-reinforced resin composite that is combined with fibers described below.

[0020] <<First photocurable resin composition>> (resin component) The first photocurable resin composition contains an epoxy compound and an oxetane compound as resin components. In this specification, the term "resin component" refers to both (a combination of) the epoxy compound and the oxetane compound.

[0021] The epoxy compound may be a known epoxy compound that is liquid or solid at room temperature, depending on the application. The epoxy compound includes at least one of a glycidyl epoxy compound and an alicyclic epoxy compound. In other words, the epoxy compound may include only a glycidyl epoxy compound, only an alicyclic epoxy compound, or both an alicyclic epoxy compound and a glycidyl epoxy compound.

[0022] Examples of glycidyl epoxy compounds include bisphenol A epoxy resins, bisphenol F epoxy resins, mixed resins of bisphenol A epoxy resins and bisphenol F epoxy resins, diglycidyl ether of bisphenol A (DGEBA), epichlorohydrin diglycidyl ether of bisphenol F, diaminodiphenylmethane epoxy resins, p-aminophenol epoxy resins, hydrogenated bisphenol A epoxy resins, hydrogenated bisphenol A diglycidyl ethers, hydrogenated bisphenol F epoxy resins, ethylene glycol diglycidyl ethers, polyethylene glycol diglycidyl ethers, and other bifunctional epoxy compounds containing two epoxy groups. Examples of monofunctional epoxy compounds containing one epoxy group include phenyl glycidyl ether, o-phenylphenol glycidyl ether, p-sec-butylphenyl glycidyl ether, p-tert-butylphenyl glycidyl ether, 2,3-propylphenyl glycidyl ether, and dibromophenyl glycidyl ether.

[0023] Examples of alicyclic epoxy compounds include bifunctional epoxy compounds containing two alicyclic epoxy groups, such as 3',4'-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate, ε-caprolactone-modified 3',4'-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate, (4R)-1,2-epoxy-4-(2-methyloxiranyl)-1-methylcyclohexane, 2,2-bis(hydroxymethyl)-1-butanol 1,2-epoxy-4-(2-oxiranyl)cyclohexane adduct, and 1,6-hexanediol diglycidyl ether. Examples of alicyclic epoxy compounds containing one alicyclic epoxy group include 1,2-epoxy-4-vinylcyclohexane, 3-methacryloyloxymethylcyclohexene oxide, 3-acryloyloxymethylcyclohexene oxide, and 3-vinylcyclohexene oxide.

[0024] Examples of compounds having an epoxy group directly or indirectly single-bonded to an aliphatic ring include hydrogenated versions of the above-mentioned compounds, epoxynorbornene, and 1,2-epoxy-4-(2-oxiranyl)cyclohexane adducts of 2,2-bis(hydroxymethyl)-1-butanol.

[0025] The content of the epoxy compound (the total content of each compound when two or more types are included) may be determined appropriately depending on the content of the oxetane compound described below, and is, for example, more than 30% by mass and less than 70% by mass relative to 100% by mass of the total amount of the resin components (epoxy compound and oxetane compound, the same applies hereinafter).

[0026] Examples of the oxetane compound include monofunctional oxetane compounds and bifunctional oxetane compounds. Examples of the monofunctional oxetane compound include 3-ethyl-3-hydroxymethyloxetane, 3-ethyl-3-(phenoxymethyl)oxetane, 2-ethylhexyloxetane, oxetanylsilsesquioxetane, phenol novolac oxetane, and 3-ethyl-3-phenoxymethyloxetane. Examples of the bifunctional oxetane compound include 3,3'-(oxybismethylene)bis(3-ethyloxetane), xylylenebisoxetane, and 3-ethyl-3{[(3-ethyloxetan-3-yl)methoxy]methyl}oxetane. Among the oxetane compounds, from the viewpoint of improving the strength (particularly crack resistance) of the cured product, monofunctional oxetane compounds are preferred, and 3-ethyl-3-hydroxymethyloxetane and 3-ethyl-3-(phenoxymethyl)oxetane are more preferred.

[0027] The content of the oxetane compound (the total content of each compound when two or more types are included) is more than 30% by mass and less than 70% by mass, based on 100% by mass of the total resin components. Since the content of the oxetane compound in the first photocurable resin composition is specified within the above range, the viscosity range described below is achieved, resulting in improved workability and improved strength of the cured product. The lower limit of the content of the oxetane compound is preferably 35% by mass or more, more preferably 40% by mass or more, based on 100% by mass of the total resin components, from the viewpoints of improving workability and reducing variations in strength between samples of the obtained cured product. Furthermore, the upper limit of the content of the oxetane compound is preferably 60% by mass or less, more preferably 50% by mass or less, based on 100% by mass of the total resin components, from the viewpoints of improving workability and cured product strength.

[0028] (additives) In addition to the above resin components, the first photocurable resin composition may contain additives such as a photoinitiator, a filler, a thickener, and silica (SiO2) described below, as long as the object of the present invention is not impaired.

[0029] The photoinitiator acts and functions to shorten the curing speed (curing time) and improve reactivity (curing method), i.e., to improve workability. The photoinitiator is not particularly limited, and examples include photopolymerization initiators such as triarylsulfonium hexafluoroantimonate mixtures. The content of the photoinitiator (the total content when two or more types are included) is, from the viewpoint of improving the above-mentioned action and function, for example, 1% by mass or more and 5% by mass or less relative to 100% by mass of the total amount of the resin components.

[0030] The filler acts and functions to reduce the curing stress caused by curing shrinkage. Examples of the filler include calcium carbonate, magnesium carbonate, barium sulfate, mica, talc, kaolin, clay, celite, barite, baryta, dolomite limestone, gypsum, hollow balloons, alumina, glass powder, aluminum hydroxide, zirconium oxide, antimony trioxide, titanium oxide, molybdenum dioxide, and iron powder.

[0031] Examples of the thickener include resin particles such as (meth)acrylic or diene core-shell type thermoplastic resins, and vinyl chloride resins.

[0032] <<Second Photocurable Resin Composition>> The second photocurable resin composition according to this embodiment contains an epoxy compound, an oxetane compound, and silica as resin components. That is, the second photocurable resin composition differs from the first photocurable resin composition in that it contains silica as an essential component. Note that, except for the following, all of the features described for the first photocurable resin composition (such as the types of components) apply to the second photocurable resin composition.

[0033] By specifying the particle size and content of silica, it acts and functions to improve the strength (especially crack resistance) of the cured product. Granular nanosilica is preferred as the silica. From the viewpoint of improving the above-mentioned action and function, the particle size of silica is preferably 10 nm or more and 350 nm or less, more preferably 20 nm or more and 300 nm or less.

[0034] The upper limit of the silica content (the total content of each silica when two or more types are included) is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less, relative to 100% by mass of the total resin components, from the viewpoint of improving the above-mentioned effects and functions. Furthermore, the lower limit of the silica content is preferably 0.5% by mass or more, more preferably 0.8% by mass or more, and even more preferably 1% by mass or more, relative to 100% by mass of the total resin components, from the viewpoint of reducing variation in strength of the cured product. Based on the above, the silica content may be 0.5% by mass or more and 30% by mass or less, relative to 100% by mass of the total resin components. For example, the content of silica having a particle size of 10 nm or more and 35 nm or less may be 0.5% by mass or more and 10% by mass or less, relative to 100% by mass of the total resin components. The content of silica having a particle size of more than 35 nm and 200 nm or less may be 1% by mass or more and 30% by mass or less, relative to 100% by mass of the total resin components. The content of silica having a particle size of more than 200 nm and not more than 350 nm may be 10% by mass or more and 30% by mass or less relative to 100% by mass of the total amount of the resin components.

[0035] The content of the epoxy compound (the total content of each when two or more types are included) may be determined appropriately depending on the content of the oxetane compound described below, and is, for example, more than 40% by mass and less than 80% by mass relative to 100% by mass of the total amount of the resin components.

[0036] The content of the oxetane compound (the total content of each compound when two or more types are included) is more than 20% by mass and less than 60% by mass, based on 100% by mass of the total resin components. Since the content of the oxetane compound in the second photocurable resin composition is specified within the above range, the viscosity range described below is achieved, resulting in improved workability and improved strength of the cured product. The lower limit of the content of the oxetane compound is preferably 25% by mass or more, more preferably 30% by mass or more, based on 100% by mass of the total resin components, from the viewpoints of improving workability and reducing variations in strength between samples of the obtained cured product. Furthermore, the upper limit of the content of the oxetane compound is preferably 50% by mass or less, more preferably 40% by mass or less, based on 100% by mass of the total resin components, from the viewpoints of improving workability and cured product strength.

[0037] The first and second photocurable resin compositions having the above-described configurations can be produced by blending the above-described components in predetermined amounts and mixing them by a known method. From the viewpoint of improving workability, the photocurable resin composition is preferably a liquid, and more preferably a one-component resin (epoxy resin).

[0038] From the viewpoint of improving workability, the viscosity of the photocurable resin composition [at room temperature (about 25°C)] is preferably 40 mPa·s or more and less than 1000 mPa·s, more preferably 40 mPa·s or more and less than 100 mPa·s or 500 mPa·s or more and less than 1000 mPa·s, and even more preferably 100 mPa·s or more and less than 500 mPa·s.

[0039] The photocurable resin composition becomes a resin cured product (photocured product) by photocuring. The photocurable resin composition has excellent workability because it can be photocured. The light source for irradiation can be, for example, ultraviolet light (UV) called UV-A or the like, with a wavelength of 315 nm to 400 nm (preferably about 365 nm). The conditions for photocuring (UV exposure) include, for example, illuminance of 10 mW / cm 2 ~5000mW / cm 2 (preferably 50mW / cm 2 ), and irradiation time (curing time): several seconds to several minutes (preferably 1 to 5 minutes). The photocuring conditions may be appropriately determined depending on the amount of light irradiation (exposure) (integrated illuminance and time). By photocuring in a short time, the photocured product of the photocurable resin composition will have high mechanical strength, with a tensile strength of 45 MPa or more.

[0040] The photocured product of the photocurable resin composition may be heat-cured as needed after photocuring. The addition of heat curing can improve the mechanical strength of the photocured product. Heat curing can be performed by a commonly known method, such as blowing hot air (at about 80°C).

[0041] The cured product of the photocurable resin composition that has been photocured (and heat-cured as necessary) preferably has a tensile strength of 45 MPa or more, more preferably 50 MPa or more, even more preferably 55 MPa or more, and even more preferably 60 MPa or more, from the viewpoint of ensuring strength (particularly crack resistance) of the cured product.

[0042] The photocured (and optionally heat-cured) cured product of the photocurable resin composition preferably has a standard deviation of tensile strength of less than 10 MPa, more preferably less than 5 MPa, in order to reduce variations in strength between samples of the resulting cured product.

[0043] <Fiber reinforced resin composite> The fiber-reinforced resin composite according to this embodiment includes a first photocurable resin composition or a second photocurable resin composition, and glass fibers. The fiber-reinforced resin composite is formed by impregnating the glass fibers with the first photocurable resin composition or the second photocurable resin composition to form a single fiber-reinforced resin. In other words, the fiber-reinforced resin composite can be considered a GFRP (glass fiber reinforced plastic) material.

[0044] The glass fiber acts and functions as a reinforcing material. The form of the glass fiber is not particularly limited as long as it can be impregnated with and retain the liquid photocurable resin composition, and any commonly known form can be used. Among these, sheet-like glass fiber, such as glass cloth, is preferred. In other words, the fiber-reinforced resin composite is preferably one in which a sheet-like glass fiber is impregnated with the photocurable resin composition.

[0045] In addition to glass fibers, the fiber-reinforced resin composite may contain, within the scope of the present invention, for example, inorganic fibers such as ceramic fibers, boron fibers, and basalt fibers; carbon fibers such as PAN (polyacrylonitrile)-based carbon fibers and pitch-based carbon fibers; synthetic organic fibers such as aramid, polyester, polyethylene, nylon, vinylon, polyacetal, PBO (polyparaphenylene benzoxazole), high-strength polypropylene, polyamide, polyarylate, and polyester; and natural fibers such as kenaf and hemp.

[0046] A commonly known method can be used to produce a fiber-reinforced resin composite. For example, a method in which a photocurable resin composition is applied or dropped onto a target location, a glass cloth is placed on the resin composition, and the composition is then impregnated with a screw roller or the like can be used; a method in which a glass cloth is placed on a target location, a photocurable resin composition is applied or dropped onto the glass cloth, and the composition is then impregnated with a screw roller or the like can be used. For example, a hand layup method, a VaRTM method, or the like can be used.

[0047] Like the photocurable resin composition, the fiber-reinforced resin composite is photocured (UV exposure) to form a fiber-reinforced cured resin (GFRP). The photocured fiber-reinforced resin composite may be heat-cured as needed after photocuring. All of the methods and conditions for photocuring and heat-curing described for the photocurable resin composition apply.

[0048] The strength of the photocured (and optionally heat-cured) fiber-reinforced resin composite is equal to or greater than the strength of the cured product of the photocurable resin composition, and from the viewpoint of ensuring the strength of the cured product (particularly crack resistance), the tensile strength is preferably 45 MPa or more, more preferably 50 MPa or more, even more preferably 55 MPa or more, and even more preferably 60 MPa or more.

[0049] <Structure repair methods> Next, a method for repairing a structure according to this embodiment will be described with reference to Figures 1 to 5. As shown in Figure 1, the method for repairing a structure is a method for repairing a damaged portion D of a structure S using a first photocurable resin composition or a second photocurable resin composition, or a fiber-reinforced resin composite containing either of them.

[0050] Examples of the structure S include relatively large structures such as the main wings and hulls of aircraft, cement-based structures (buildings, etc.), their joints and piping (pipes), and wind power generator blades. In particular, wind power generator blades, which are required to be inspected annually, are mostly made of GFRP, and therefore the structure repair method according to this embodiment can be suitably used to repair damage to the blades.

[0051] The method for repairing a structure according to this embodiment includes a pre-painting step S2 and a painting step S3. The method for repairing a structure may also include a grinding step S1 and a thermal curing step S4, as necessary.

[0052] Grinding process (optional process) The grinding step S1 is performed, if necessary, before the pre-coating step S2. As shown in Fig. 1, the grinding step S1 grinds away damaged portions D of the structure S to form recesses R. The grinding step S1 makes the surface of the damaged portions D of the structure S a smooth, concave surface, which improves the work efficiency of the subsequent pre-coating step S2 and coating step S3 and also improves the adhesive strength between the surface and the second photocured material layer 2, which will be described later.

[0053] <Pre-painting process> As shown in Fig. 2, in the pre-coating step S2, a photocurable resin composition is coated (applied) on the surface of the damaged portion D of the structure S or on the surface of the recess R formed in the grinding step S1 so as to cover the damaged portion D, and then photocured (UV exposed). This forms a first photocured product layer (pre-adhesion layer) 1, which is a photocured product of the photocurable resin composition, on the surface. The adhesive strength between the surface and the second photocured product layer 2 is further improved via the first photocured product layer.

[0054] <Painting process> 3 and 4, in the coating step S3, a fiber-reinforced resin composite, which is made by impregnating a sheet of glass fiber with a photocurable resin composition using a hand layup method or a VaRTM method, is coated (applied) onto the surface of the first photocured material layer 1 formed in the pre-coating step S2, and then photocured (UV exposed). As a result, at least one second photocured material layer 2, which is a photocured product of the fiber-reinforced resin composite, is formed on the surface of the first photocured material layer 1.

[0055] As shown in FIG. 3 , first, a glass cloth (glass fiber sheet) G cut to a size larger than the first photocured layer 1 (damaged portion D) is placed on the surface of the first photocured layer 1. Next, the glass cloth G is impregnated with a photocurable resin composition (resin) to form one uncured layer of the fiber-reinforced resin composite. At this time, a peel ply P may be placed on the resin-impregnated glass cloth G, and the resin may be impregnated throughout the glass cloth G using a screw roller (not shown). Excess resin may be pushed out from the glass cloth G. Finally, the uncured layer is photocured (UV-exposed). This forms one second photocured layer 2a (GFRP) on the surface of the first photocured layer 1. After UV exposure, the peel ply P can be peeled off from the second photocured layer 2a. The photocuring method is not particularly limited, and commonly known methods can be used, such as UV exposure using a commercially available UV-curing handheld light. The photo-curing time can be determined appropriately depending on the size (area), thickness (total thickness) and number of layers of the second photo-cured layer 2, and is not particularly limited. For example, if the repair size is 40 cm x 40 cm and the total thickness is about 5 mm, the photo-curing time is about 1 to 5 minutes.

[0056] By repeating the above operation multiple times depending on the size (depth) of the damaged area D, at least one layer of second photocured material layer 2 (GFRP) is formed as shown in Figure 4 (in Figure 4, a five-layer laminate in which second photocured material layers 2a to 2e are stacked in order from the bottom).

[0057] In the painting step S3, it is preferable to form a plurality of second photocured material layers 2 by stacking the fiber-reinforced resin composites by hand lay-up and photocuring each layer.

[0058] <<Variations in the painting process>> In the coating step S3, when the total thickness of the multiple second photocured material layers 2 is, for example, 1.5 mm or less, instead of photocuring each layer individually, a laminate of multiple fiber-reinforced resin composites may be formed and then the laminate may be photocured all at once. Also, in the coating step S3, instead of impregnating the glass cloth G with the photocurable resin composition at the repair site, a fiber-reinforced resin composite may be prepared in advance and placed on the surface of the first photocured material layer 1.

[0059] 《Thermosetting process (optional process)》 The thermal curing step S4 is performed after the coating step S3, as needed. As shown in FIG. 5, the thermal curing step S4 involves thermal curing after photocuring. In other words, the laminate of the first photocured layer 1 and the second photocured layer 2 is further thermally cured. Complete curing of the laminate improves the strength of the second photocured layer 2. The thermal curing step S4 can be considered a method of simultaneously heating the multiple second photocured layers 2. The thermal curing step S4 may be performed immediately after UV curing (the coating step S3). The thermal curing method is not particularly limited, and generally known methods can be used, such as blowing hot air Ha using a commercially available heater. The heating temperature for thermal curing is, for example, approximately 50 to 100°C. The thermal curing time can be determined appropriately depending on the size (area), thickness (total thickness), and number of layers of the second photocured layer 2, but is not particularly limited. For example, if the repair size is 40 cm x 40 cm and the total thickness is approximately 5 mm, the thermal curing time is approximately 1 to 5 minutes.

[0060] <Summary> The first and second photocurable resin compositions according to the present embodiment are one-component UV-curable epoxy resins that have mechanical strength performance equivalent to that of two-component curable resins, and are therefore useful as matrix resins for fiber-reinforced resin composites, which are materials for GFRP and the like. The fiber-reinforced resin composite according to this embodiment is formed by impregnating glass fibers with the first photocurable resin composition or the second photocurable resin composition, and is therefore useful as a repair material for structures that use GFRP (such as wind turbine blades). The structure repair method according to this embodiment uses a one-component resin, a first photocurable resin composition or a second photocurable resin composition, and a fiber-reinforced resin composite containing the same. This eliminates the need to mix the resin at the repair site, and the resin can be photocured in a short time (a few minutes) by irradiation with UV light (the reaction is completed in a short time). Furthermore, even when thermally cured, the reaction is completed in a short time (a few minutes). Therefore, with the structure repair method according to this embodiment, the repair work that currently takes approximately three days to inspect and repair the blades of a single wind turbine can be completed on the same day (in one day). [Example]

[0061] The present disclosure will be described below based on examples. Note that the present disclosure is not limited to the following examples, and the following examples can be modified or changed based on the spirit of the present disclosure, and such modifications are not excluded from the scope of the present disclosure.

[0062] <First Example Series> [Preparation of first photocurable resin composition] The various components shown in Table 1 were blended in the amounts shown in Table 1 and mixed to prepare each photocurable resin composition.

[0063] 〔evaluation〕 The first photocurable resin composition and its cured product were evaluated as follows. The results are shown in Table 1. For each evaluation, a grade of Fair or better was considered to be acceptable. Furthermore, a photocurable resin composition that had both Fair or better workability and mechanical strength (their average values ​​and standard deviations) was considered to be an acceptable product.

[0064] (Workability) The viscosity of the photocurable resin composition was measured at room temperature (25° C.) using an E-type viscometer, and the workability was evaluated based on the following evaluation criteria. Evaluation Criteria ○: Viscosity is 100 mPa·s or more and less than 500 mPa·s. △: Viscosity is 40 mPa·s or more but less than 100 mPa·s or 500 mPa·s or more but less than 1000 mPa·s. ×: Viscosity is less than 40 mPa·s or 1000 mPa·s or more.

[0065] (mechanical strength) The photocurable resin composition was applied under an illumination intensity of 3000 mW / cm 2 After photocuring at 40°C, the resin was thermally cured for 30 minutes at 80°C to obtain a cured product of the photocurable resin composition (corresponding to the "first photocured product layer"). Using this cured product, tensile strength was measured under the following measurement conditions, and mechanical strength was evaluated based on the following evaluation criteria. <<Measurement conditions>> Test piece size: Width 25mm, length 100mm (handle ends 25mm, measurement length 50mm), thickness 0.3mm Measurement equipment: Universal testing machine Pulling speed: 5mm / min Measurements: 5 times (n=5) Evaluation Criteria Mechanical strength is considered to be acceptable if both (1) and (2) below are fair or better. (1) Average tensile strength ◎: The average tensile strength is 60 MPa or more. ◯: The average tensile strength is 55 MPa or more and less than 60 MPa. △: The average value of the tensile strength is 45 MPa or more and less than 55 MPa. ×: The average tensile strength is less than 45 MPa. (2) Standard deviation of tensile strength ○: The standard deviation of the tensile strength is less than 5 MPa. △: The standard deviation of the tensile strength is 5 MPa or more and less than 10 MPa. ×: The standard deviation of the tensile strength is 10 MPa or more.

[0066] [Table 1]

[0067] The various materials listed in Table 1 are as follows: Glycidyl epoxy compound: JER828 (manufactured by Mitsubishi Chemical Corporation), bisphenol A epoxy resin (liquid). Alicyclic epoxy compounds: Ceox2021P (manufactured by Daicel Corporation), 3',4'-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate (bifunctional). Oxetane compound A: OXT-101 (manufactured by Toagosei Co., Ltd.), 3-ethyl-3-hydroxymethyloxetane (monofunctional). Oxetane compound B: OXT-211 (manufactured by Toagosei Co., Ltd.), 3-ethyl-3-(phenoxymethyl)oxetane (monofunctional). Photoinitiator: AT-6976 (Tomoe Engineering Co., Ltd.), triarylsulfonium hexafluoroantimonate mixture.

[0068] <Considerations on the first example series> From Table 1, it was confirmed that each Example (first photocurable resin composition) in which the content of the oxetane compound was more than 30 mass% and less than 70 mass% relative to 100 mass% of the total amount of the resin components had both excellent workability and high strength of the cured product. On the other hand, it was confirmed that the comparative examples in which the oxetane compound content was outside the above range were inferior in at least one of workability and mechanical strength. Specifically, it was found that with regard to workability, when the content was small or large (Comparative Examples 1, 2, 4, and 5), workability decreased due to an increase or decrease in viscosity. With regard to mechanical strength, it was found that the comparative examples 1 to 3 in which the content was low had a large standard deviation of mechanical strength, which may result in variations in strength after curing. On the other hand, it was found that the comparative examples 4 to 5 in which the content was high had a decrease in mechanical strength (its average value) itself. From the above, it is considered that the first photocurable resin composition (each example) is suitably used for fiber-reinforced resins, and is useful for fiber-reinforced resin composites containing the same and for methods for repairing structures using these.

[0069] <Second Example Series> [Preparation of second photocurable resin composition] The various components shown in Table 2 were blended in the amounts shown in Table 2 and mixed to prepare each photocurable resin composition.

[0070] 〔evaluation〕 The second photocurable resin composition and its cured product were evaluated in the same manner as in the first example series. The results are shown in Table 2.

[0071] [Table 2]

[0072] The various materials listed in Table 2 are as follows. Note that, except for the silica shown below, the materials are the same as those used in the first example series. · Silica (particle size 20nm): Nanopox E470 Evonik Japan Co., Ltd. · Silica (particle size 50nm): YA050-SM1 Admatechs Co., Ltd. · Silica (particle size 200nm): SOE1 Admax Co., Ltd.

[0073] <Discussion of the second example series> Table 2 shows that each example (second photocurable resin composition) further containing silica and having an oxetane compound content of more than 20% by mass and less than 60% by mass relative to 100% by mass of the total resin components has excellent workability and high strength of the cured product, similar to the first photocurable resin composition. It was also confirmed that the second photocurable resin composition has improved mechanical strength compared to the first photocurable resin composition. On the other hand, it was confirmed that each of the comparative examples in which the content of the oxetane compound was outside the above range was inferior in at least one of workability and mechanical strength. The tendency (reason) for this was the same as that for the first photocurable resin composition. From the above, it is considered that the second photocurable resin composition (each example) further containing silica is also suitable for use in fiber-reinforced resins, and is useful for fiber-reinforced resin composites containing the same and for methods for repairing structures using these.

[0074] <Third Example Series> Example 31 (Formation of First Photocured Material Layer) A first photocured layer made of a photocurable resin composition was formed on the surface of the object to be repaired. Specifically, a peel ply was first applied to the surface of the object to be repaired, and the photocurable resin composition (resin) of Example 12 (Table 2) was then applied. Subsequently, UV light was applied to the coated surface at an illuminance of 3000 mW / cm. 2 After curing, the peel ply was peeled off from the cured product to form a thin resin layer (first photocured product layer) on the surface of the object to be repaired.

[0075] (Formation of second photocured layer) Furthermore, a second photocured layer made of a fiber-reinforced resin composite was formed on the surface of the first photocured layer. Specifically, first, one layer of 4-axis 880G glass cloth (sheet-like glass fiber) was placed on the surface of the first photocured layer so as to cover the first photocured layer. Next, the photocurable resin composition of Example 12 was impregnated into the glass cloth by a hand layup method to form a fiber-reinforced resin composite. A peel ply was attached to the surface of the fiber-reinforced resin composite, and then the surface was irradiated with UV light under the same conditions as above to cure the fiber-reinforced resin composite. After curing, the peel ply was peeled off from the cured product to form a second photocured layer (GFRP) on the surface of the first photocured layer.

[0076] Comparative Example 31 (Formation of second photocured layer) A second photocured layer made of a fiber-reinforced resin composite was formed on the surface of the object to be repaired. Specifically, first, one layer of glass cloth 4-axis 880G was placed on the surface of the object to be repaired. Next, the glass cloth was impregnated with the photocurable resin composition of Example 12 using a hand layup method to form a fiber-reinforced resin composite. A peel ply was attached to the surface of the fiber-reinforced resin composite, and then the surface was irradiated with UV light under the same conditions as above to cure the fiber-reinforced resin composite. After curing, the peel ply was peeled off from the cured product to form a second photocured layer (GFRP) directly on the surface of the object to be repaired.

[0077] 〔evaluation〕 The adhesiveness of the second photocured material layer was evaluated based on the following evaluation criteria. Evaluation Criteria When inserting the blade of a cutter into the edge of the second photocured material layer and trying to peel the second photocured material layer off the surface of the object to be repaired, ◯: The surface of the object to be repaired and the second photocured material layer are strongly bonded to each other, so much so that the cutter blade cannot be inserted even 1 mm. ×: By inserting the cutter blade, peeling progressed to the interface between the surface of the object to be repaired and the second photocured material layer, and the layer could be peeled off.

[0078] <Results and Discussion of the Third Example Series> The adhesiveness of the second photocured material layer was evaluated as "good" in Example 31 and "bad" in Comparative Example 31. These results confirmed that Example 31, in which a first photocured material layer was formed as a pre-coat between the surface of the object to be repaired and the second photocured material layer, had superior adhesiveness of the second photocured material layer compared to Comparative Example 31, which did not have a first photocured material layer. In other words, it was confirmed that the surface of the object to be repaired and the second photocured material layer were strongly adhered via the first photocured material layer. From the above, it can be seen that the method for repairing a structure in which a first photocured material layer is formed (Example 31) is useful as a method for repairing target structures (especially blades of wind turbine generators) because the second photocured material layer is less likely to peel off after repair. [Explanation of symbols]

[0079] D Damaged part G Glass cloth (sheet-shaped glass fiber) Ha hot air P Peel ply R recess S structure S1 Grinding process S2 Pre-painting process S3 Painting process S4 Heat curing process 1 First photocured material layer 2,2a~2e 2nd photocured material layer

Claims

1. A photocurable resin composition used in a fiber reinforced resin, Contains an epoxy compound and an oxetane compound as resin components, A photocurable resin composition for fiber-reinforced resins, characterized in that the content of the oxetane compound is more than 30% by mass and less than 70% by mass relative to 100% by mass of the total amount of the resin components.

2. A photocurable resin composition used in a fiber reinforced resin, The composition contains an epoxy compound, an oxetane compound, and silica as resin components, A photocurable resin composition for fiber-reinforced resins, characterized in that the content of the oxetane compound is more than 20% by mass and less than 60% by mass relative to 100% by mass of the total amount of the resin components.

3. 3. The photocurable resin composition for fiber-reinforced resin according to claim 2, wherein the content of the silica is 30% by mass or less relative to 100% by mass of the total amount of the resin components.

4. 4. The photocurable resin composition for fiber-reinforced resins according to claim 2, wherein the particle diameter of the silica is 10 nm or more and 350 nm or less.

5. 3. The photocurable resin composition for fiber-reinforced resin according to claim 1, wherein the epoxy compound comprises at least one selected from the group consisting of a glycidyl-type epoxy compound and an alicyclic epoxy compound.

6. A fiber-reinforced resin composite comprising the photocurable resin composition according to claim 1 or 2 and glass fibers.

7. 7. The fiber-reinforced resin composite according to claim 6, wherein the glass fiber sheet is impregnated with the photocurable resin composition.

8. A method for repairing a damaged portion of a structure using a photocurable resin composition, comprising: The photocurable resin composition contains an epoxy compound and an oxetane compound as resin components, A method for repairing a structure, comprising applying the photocurable resin composition to the surface of the damaged portion and photocuring the composition to form a first photocured layer.

9. The method for repairing a structure according to claim 8, characterized in that at least one second photocured material layer is formed by coating the surface of the first photocured material layer with a fiber-reinforced resin composite obtained by impregnating a sheet-shaped glass fiber with the photocurable resin composition by a hand lay-up method or a VaRTM method, and then photocuring the composite.

10. 10. The method for repairing a structure according to claim 9, wherein the fiber-reinforced resin composite is stacked by a hand layup method and photocured layer by layer to form multiple layers of the second photocured material.

11. 11. The method for repairing a structure according to claim 9, wherein the second photocured layer is thermally cured after being completely formed.

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