Surface protective material, molded body, and surface protective fiber-reinforced composite material

Abstract

The present invention addresses the problem of providing an epoxy resin composition which has excellent light resistance, is capable of protecting the surface of a base material of a fiber-reinforced composite material and preventing deterioration due to light by being disposed on the outermost surface of a composite material precursor, is capable of suppressing pinholes caused by leaving a surface protective material at room temperature, is capable of covering the whole surface of the fiber-reinforced composite material without a mixture defect by using the surface protective material on the surface of the composite material precursor, and is capable of imparting good appearance and sound light resistance.　The present invention provides a surface protective material which is obtained by at least partially impregnating a nonwoven fabric base material with an epoxy resin composition that contains constituent elements (A) to (C), wherein the content of the epoxy resin composition is within the range of 75 mass% to 98 mass%. (A) a non-aromatic epoxy resin, (B) a thixotropic agent, (C) a curing agent

Description

Surface protection material, molded body, and surface protection fiber-reinforced composite material

[0001] The present invention relates to a surface protective material and a surface-protected fiber-reinforced composite material containing an epoxy resin composition.

[0002] Fiber-reinforced composite materials are often used in products requiring high specific modulus and specific strength, such as aircraft components, wind turbine blades, automobile exterior panels, and laptop computer housings. However, typical fiber-reinforced composite materials have poor light resistance and deteriorate when their surfaces are exposed to light (mainly UV). Therefore, in recent years, there has been an increasing demand for fiber-reinforced composite materials with light resistance. Some resin compositions with light resistance use non-aromatic epoxy resins.

[0003] Patent Document 1 proposes an encapsulant using a non-aromatic epoxy resin composition, and Patent Document 2 proposes a coating agent using an epoxy resin composition containing a non-aromatic epoxy resin. In Patent Document 1, the epoxy composition is used alone as an encapsulant for photoelectric conversion elements typified by LEDs, and is cured to encapsulate the photoelectric conversion elements.

[0004] Patent Document 2 describes a method in which an epoxy resin composition containing a non-aromatic epoxy resin is applied using a spray or a bar coater and then cured to form a surface protective material.

[0005] Furthermore, Patent Document 3 describes a fiber-reinforced composite material, and describes an example in which an epoxy resin composition containing a non-aromatic epoxy resin is included. Specifically, in order to obtain a material with low tack and low resin flow, the epoxy resin composition containing a low-viscosity non-aromatic epoxy is pre-cured in a resin film, and then the resin film is impregnated with a nonwoven fabric to form a prepreg.

[0006] JP 2003-26763 A International Publication No. 2021 / 153487 International Publication No. 2022 / 113976

[0007] In order to impart light resistance to a fiber-reinforced composite material, the present inventors have investigated a technique of forming a layer of a cured epoxy resin composition containing a non-aromatic epoxy resin on the surface (the side irradiated with UV) of the fiber-reinforced composite material, and have investigated a technique of laminating a material in which a nonwoven fabric substrate is at least partially impregnated with an epoxy resin composition, i.e., a surface protective material, on the surface of the fiber-reinforced composite material.

[0008] In the process, they discovered that when such surface protection materials are stored for a predetermined period of time, it becomes an issue to prevent the formation of "pinholes," which are usually relatively small holes that penetrate the material.

[0009] Neither of the inventions of Patent Documents 1 nor 2 proposes any improvement from the viewpoint of improving the handleability of an epoxy resin composition containing a non-aromatic epoxy resin when used as a sealant or a protective material.

[0010] Patent Document 3 describes laminating and curing only a prepreg containing a non-aromatic epoxy resin, but does not describe the idea of ​​laminating such a prepreg on the surface of another prepreg to protect the surface of the resulting fiber-reinforced composite material and impart light resistance. Furthermore, the invention of Patent Document 3 does not describe any problems that may arise when storing a non-aromatic epoxy resin-containing prepreg using a nonwoven fabric substrate for a predetermined period of time, and does not address the issue of pinholes mentioned above.

[0011] Therefore, an object of the present invention is to provide a surface protection material that, when used with a nonwoven fabric substrate and a non-aromatic epoxy resin, can suppress pinholes even when stored at room temperature for a certain period of time, has good handleability, and can form a surface-protected fiber-reinforced composite material that has excellent appearance and light resistance after molding.

[0012] 1. A surface protective material comprising a nonwoven fabric substrate at least partially impregnated with an epoxy resin composition comprising components [A] to [C], wherein the content of the epoxy resin composition is in the range of 75 to 98 mass %. [A] Non-aromatic epoxy resin [B] Thixotropic agent [C] Curing agent 2. The surface protective material according to 1 above, wherein the nonwoven fabric substrate comprises glass fiber. 3. The surface protective material according to 1 or 2 above, wherein the nonwoven fabric substrate comprises fibers having a fiber diameter of 3 to 20 μm. 4. The surface protective material according to any one of 1 to 3 above, wherein the nonwoven fabric substrate comprises short fibers having a fiber length of 2 to 30 mm. 5. The surface protective material according to any one of 1 to 4 above, wherein the WPU value is 0.5 to 10%. 6. The surface protective material according to any one of 1 to 5 above, wherein there is a difference in the degree of exposure of the nonwoven fabric substrate on both surfaces of the surface protective material. 7. 7. The surface protective material according to any one of 1 to 6 above, wherein the orientation distribution f of the reinforcing fibers in the nonwoven fabric substrate is 0.300 to 0.637. 8. The surface protective material according to any one of 1 to 7 above, wherein the voids in the nonwoven fabric substrate are 3 to 35%. 9. The surface protective material according to any one of 1 to 8 above, wherein the epoxy resin composition has a Casson yield value at 74°C in the range of 70 to 1000 Pa. 10. The component [B] is a resin having a specific surface area of ​​60 to 300 m ２ / g. 11. The surface protective material according to any one of 1 to 10 above, wherein component [B] is contained in an amount of 3 to 14 parts by mass when the total amount of the epoxy resin is taken as 100 parts by mass. 12. The surface protective material according to any one of 1 to 11 above, further comprising component [D], wherein the amount of component [D] is 20 to 70 parts by mass when the total amount of the epoxy resin is taken as 100 parts by mass. [D] Non-aromatic thermoplastic resin 13. A molded article obtained by curing the surface protective material according to any one of 1 to 12 above or a laminate comprising a plurality of such surface protective materials. 14. A surface-protected fiber-reinforced composite material obtained by curing a surface-protective-material-attached fiber-reinforced composite material precursor, which is a single layer of prepreg or a laminate comprising a plurality of prepreg layers, and having the surface protective material according to any one of 1 to 12 above attached to the outermost surface on one or both sides of the fiber-reinforced composite material precursor.

[0013] According to the present invention, it is possible to provide a surface protective material that contains an epoxy resin composition having excellent light resistance and that can suppress pinholes after storage at room temperature.

[0014] 1A and 1B are cross-sectional views in the thickness direction of a surface protective material of the present invention, showing a large difference in the degree of exposure of the nonwoven fabric substrate on both surfaces, and a cross-sectional view in the thickness direction of a surface protective material of the present invention, showing no difference in the degree of exposure of the nonwoven fabric substrate on both surfaces.

[0015] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. Furthermore, when an essential range, a preferred range, etc. for a certain physical property or characteristic is expressed as multiple numerical ranges, any upper limit value and any lower limit value included in those multiple ranges can be combined in any way unless otherwise specified.

[0016] Unless otherwise specified, the evaluation according to the present invention is carried out under the conditions of a temperature of 23° C. and a humidity of 50% RH.

[0017] "Overview" The surface protective material of the present invention is a material in which a nonwoven fabric substrate is at least partially impregnated with an epoxy resin composition. "At least partially impregnated" here means that the nonwoven fabric substrate in the surface protective material may have a region in the thickness direction that is not wetted with the epoxy resin composition. A surface protective material with a Water Pick Up (WPU) of 0.05 to 20%, which indicates the degree of water uptake, is considered to be partially impregnated. In a water uptake test to measure WPU, water is not absorbed into the epoxy resin composition in the surface protective material, but is absorbed into the reinforcing fiber portion that is not wetted with the epoxy resin composition. Therefore, a surface protective material with a WPU of 0.05% or more indicates a material in which the nonwoven fabric substrate in the surface protective material has a region in the thickness direction that is not wetted with the epoxy resin composition. In the present invention, a fiber-reinforced composite material precursor (hereinafter sometimes referred to as a composite material precursor) is an intermediate material formed by laminating a single layer or multiple layers of a material in which reinforcing fibers are impregnated with a thermosetting resin, i.e., a prepreg. A fiber-reinforced composite material is a material obtained by curing a composite material precursor. A surface-protected fiber-reinforced composite material is a material obtained by curing a surface-protective-material-attached fiber-reinforced composite material precursor, in which a surface protective material is disposed on the surface of a composite material precursor.

[0018] To achieve good light resistance, the surface protective material of the present invention requires that the epoxy resin composition contain a non-aromatic epoxy resin. This is because the inclusion of a non-aromatic epoxy resin makes the epoxy resin composition less susceptible to degradation due to light absorption and provides light resistance. In the present invention, an "aromatic compound" refers to a compound having a ring structure that satisfies Hückel's rule, such as a compound containing an aromatic hydrocarbon or an aromatic heterocycle in its chemical structure, and an "aromatic epoxy resin" refers to an epoxy resin having a ring structure that satisfies Hückel's rule. A "non-aromatic compound" refers to a compound that does not have a ring structure that satisfies Hückel's rule, such as a compound composed solely of saturated hydrocarbons or saturated heterocycles, and a "non-aromatic epoxy resin" refers to an epoxy resin that does not have a ring structure that satisfies Hückel's rule.

[0019] The surface protective material of the present invention includes a nonwoven fabric substrate for better handling, because the use of a nonwoven fabric substrate makes it less susceptible to dimensional changes (distortion) during handling compared to a woven fabric substrate.

[0020] However, surface protective materials in which a nonwoven fabric substrate is impregnated with an epoxy resin composition containing a non-aromatic epoxy resin may develop pinholes, where the resin is absent in the thickness direction, during storage at room temperature. When such pinholes develop, the fiber-reinforced composite material, which has poor light resistance, is exposed to the surface at the pinhole-prone portion of the surface-protected fiber-reinforced composite material, resulting in locally insufficient light resistance.

[0021] The present inventors believe that the pinhole phenomenon caused by the flow of epoxy resins in epoxy resin compositions containing non-aromatic epoxy resins is due to the weak intermolecular interactions of non-aromatic epoxy resins, which are unable to resist a phenomenon known as "springback" that occurs in the reinforcing fibers constituting the nonwoven fabric substrate, resulting in the formation of pinholes. Hereinafter, "springback" refers to the phenomenon in which a deformed material returns to its original shape. During the production process, the pressure, heat, and other factors applied to the surface protective material can cause the nonwoven fabric substrate contained in the surface protective material to be deformed in a manner that crushes it in the thickness direction. Therefore, when the surface protective material is left at room temperature, the reinforcing fibers gradually spring back, causing the crushed thickness to return to its original thickness. Hereinafter, the springback of the reinforcing fibers of the nonwoven fabric substrate described above may be simply referred to as "springback."

[0022] Therefore, the present inventors have found that the occurrence of pinholes can be suppressed by including a thixotropic agent in an epoxy resin composition and setting the content of the epoxy resin composition in a surface protective material to 75 to 98 mass %.

[0023] The content of the epoxy resin composition in the surface protective material of the present invention (hereinafter referred to as the resin content) must be 75 to 98% by mass, preferably 80 to 98% by mass, and more preferably 85 to 98% by mass. When the resin content is 75% by mass or more, the epoxy resin composition can efficiently suppress springback and prevent pinholes from occurring. Furthermore, when the resin content is 98% by mass or less, the content of reinforcing fibers can be relatively increased, resulting in increased rigidity of the surface protective material and achieving good handleability.

[0024] The resin content (mass%) is expressed as a percentage by dividing the basis weight of the epoxy resin composition in the surface protective material by the basis weight of the surface protective material, and when the surface protective material consists only of an epoxy resin composition and a nonwoven fabric substrate, it can be calculated using the following formula: (basis weight of resin) / (basis weight of resin + basis weight of nonwoven fabric substrate)×100, where the resin basis weight is the basis weight of the epoxy resin composition.

[0025] Nonwoven fabric substrate weight (unit: g / m ２ ) and resin basis weight (unit: g / m ２ ) is determined by the following method. First, the surface protection material is cut into a 10 cm x 10 cm square sample, its mass is measured, and the area (1 x 10 －２ m ２ ) to calculate the basis weight of the surface protective material. Next, the sample is immersed in a solvent such as acetone and stirred, and then filtered (for example, filtered using a 0.2 μm PTFE filter), and the filtered material is thoroughly washed with the solvent. Thereafter, the solvent is completely removed in an oven (for example, when acetone is used, the solvent is removed by leaving it in an oven set to 100° C. for 15 minutes or more), and only the nonwoven fabric substrate is extracted. The mass of the extracted nonwoven fabric substrate is measured, and the area (1 × 10 －２ m ２ When the surface protective material consists only of an epoxy resin composition and a nonwoven fabric substrate, the resin basis weight is calculated by subtracting the nonwoven fabric substrate basis weight from the surface protective material basis weight.

[0026] Any of the above-mentioned basis weights was measured at five randomly selected points on the surface protection material, and the above-mentioned 1 × 10 －２ m ２If it is necessary to measure the density of the nonwoven fabric substrate, similarly, 1 × 10 －２ m ２ Five samples are taken, and the average value of each sample (a total of five measurements) is used. －２ m ２ If it is not possible to take five samples of the area, the value obtained from a sample of the area that can be taken may be used.

[0027] "Surface protective material" In the present invention, it is preferable that there is a difference in the degree of exposure of the nonwoven fabric substrate between one surface and the other surface of the surface protective material. In this specification, one surface and the other surface of the surface protective material may also be referred to as both surfaces of the surface protective material. As shown in the side cross section in Figure 1, when the degree of exposure of the nonwoven fabric substrate is high on one surface of the surface protective material, pinholes can be preferably suppressed compared to when there is no exposure of the nonwoven fabric substrate (or the degree of exposure is low) on both surfaces of the surface protective material, as shown in the side cross section in Figure 2. This is because, in the thickness direction of the surface protective material, if there is a region where the nonwoven fabric substrate is not impregnated with the epoxy resin composition, i.e., where the nonwoven fabric substrate is exposed, the springback of the nonwoven fabric substrate in the exposed portion does not affect the epoxy resin composition in that region.

[0028] To produce a surface protective material in which the nonwoven fabric substrate is highly exposed on only one side of the surface protective material, as shown in Figure 1, it is preferable to impregnate the nonwoven fabric substrate with the epoxy resin composition from only one side (single-sided impregnation). Impregnating only one side of the nonwoven fabric substrate with the epoxy resin composition facilitates exposing the nonwoven fabric substrate on one side of the surface protective material, as shown in Figure 1. Hereinafter, the side of the nonwoven fabric substrate that is in the resin and not exposed will be referred to as the resin side (reference numeral 5 in Figures 1 and 2), and the side on which the nonwoven fabric substrate is exposed will be referred to as the fiber side (reference numeral 4 in Figure 1). In the case of single-sided impregnation, it is easy to form a resin side on one side and a fiber side on the opposite side. The exposure of the nonwoven fabric substrate on the fiber side of the surface protective material varies depending on the degree of impregnation of the nonwoven fabric substrate with the epoxy resin composition (which depends on the impregnation pressure and heating conditions). Hereinafter, the degree of impregnation of the nonwoven fabric substrate with the epoxy resin composition will be abbreviated as the impregnation degree. Generally, as the degree of impregnation increases, the difference in the degree of exposure of the nonwoven fabric substrate on both sides decreases, approaching the state shown in FIG.

[0029] The degree of exposure of the nonwoven fabric substrate can be determined using the tack determined by a method (rolling tack test) in accordance with ASTM D3121-94:1999 as an index. This is because the tack of an epoxy resin composition is usually higher than that of a nonwoven fabric substrate, and therefore the tack decreases as the exposure of the nonwoven fabric substrate increases. The rolling ball tack test is measured in accordance with ASTM D3121:1999, and an apparatus used for the measurement can be, for example, a PI-1202 rolling ball tack tester (manufactured by Tester Sangyo Co., Ltd., inclined surface 165 mm, angle 21.5°, steel ball 7 / 16 inch). Other details of the measurement method are as described in the examples, but different methods may be used as long as the same results can be obtained under different conditions, including the double-sided tape attached to the workbench of the apparatus.

[0030] In the present invention, the distance that the ball rolls in a rolling ball tack test on at least one surface of the surface protective material is preferably 70 mm or more, more preferably 90 mm or more, and even more preferably 150 mm or more. When the distance that the ball rolls is 70 mm or more, the degree of exposure of the nonwoven fabric substrate increases, and the pinholes can be suppressed. By exposing the nonwoven fabric substrate on the surface to be evaluated, it becomes easy to adjust the ball rolling distance to the above-mentioned range.

[0031] On the other hand, in the present invention, the rolling distance of a ball on only one side of the surface protective material in a rolling ball tack test is preferably 250 mm or less, more preferably 200 mm or less, and even more preferably 100 mm or less. When the rolling distance of the ball is 250 mm or less, the surface protective material has sufficient tack, excellent adhesion to the composite material precursor, and achieves even better handleability.

[0032] In the present invention, it is preferable that the nonwoven fabric substrate has a large exposure on one side and a small exposure on the other side, and has sufficient tack, thereby achieving good handleability while effectively suppressing pinholes.

[0033] Furthermore, when one side of a surface protective material is a fiber side and the other side is a resin side, if, in a rolling ball tack test, the fiber side is tack-free and the distance that a ball rolls on the resin side is 90 to 250 mm, or the difference in the distance that a ball rolls on the fiber side and the resin side is 50 to 180 mm, it can be said that there is a sufficient difference in the degree of exposure of the nonwoven fabric substrate on both surfaces of the surface protective material, and good handleability is achieved while effectively suppressing the pinholes.

[0034] In the surface protective material of the present invention, it is preferable that the nonwoven fabric substrate has a certain amount of area that is not impregnated with the epoxy resin composition, from the viewpoint of more easily suppressing pinholes. This is because, even if the nonwoven fabric substrate springs back in this area, it will not affect the epoxy resin composition. Specifically, the WPU of the epoxy resin composition applied to the nonwoven fabric substrate is preferably 0.5 to 10%, more preferably 1.5 to 10%, even more preferably 2.0 to 10%, and even more preferably 2.0 to 7.0%. A WPU of 0.5% or more is preferable because pinholes can be more easily suppressed. Furthermore, a WPU of 10% or less suppresses adhesion (contamination) of the epoxy resin composition to gloves and other items during the process of attaching the surface protective material to a composite material precursor, thereby achieving even better handleability.

[0035] The WPU can be determined by a water uptake test, and the details of the measurement method are as described in the Examples.

[0036] In the surface protective material of the present invention, the maximum diameter of the pinholes is preferably 400 μm or less, more preferably 200 μm or less, and even more preferably 0 μm. If the maximum diameter of the pinholes is 400 μm or less, the pinholes are easily closed by the flow of the epoxy resin composition during curing, and the surface of the surface-protected fiber-reinforced composite material can be sufficiently covered with the surface protective material after curing, making it possible to impart light resistance to the entire surface.

[0037] The maximum diameter of the pinholes can be determined by observation with an optical microscope, and can be measured using, for example, a VHX-5000 (manufactured by Keyence Corporation). Details of other measurement methods are as described in the examples, but different methods may be used as long as the same results can be obtained. "Nonwoven Fabric Substrate" In the present invention, the nonwoven fabric substrate refers to a reinforcing fiber sheet, web, or pad, excluding woven fabrics, taffeta, and felted felt, in which the reinforcing fibers are oriented unidirectionally or randomly and the reinforcing fibers are bonded together by any one or a combination of entanglement, fusion, and adhesion. The manufacturing method of the nonwoven fabric substrate is not particularly limited, but the web can be formed by a dry method, a wet method, or a spunbond method, and the reinforcing fibers can be bonded together by needle punching, chemical bonding, thermal bonding, spunlace, etc.

[0038] The basis weight of the nonwoven fabric substrate is 15 to 50 g / m ２ It is preferable that the density is 15 to 30 g / m ２ More preferably, it is 15 to 25 g / m ２ It is more preferable that the nonwoven fabric substrate has a basis weight of 15 g / m ２ When the nonwoven fabric substrate has a basis weight of 50 g / m or more, the rigidity of the surface protective material is increased, and better handleability can be achieved. ２ If the thickness is less than this, springback is small and it is easy to suppress the occurrence of pinholes.

[0039] The reinforcing fibers constituting the nonwoven fabric substrate used in the present invention may be in the form of either continuous fibers or short fibers, but short fibers are preferred because the reinforcing fibers in the surface protective material overlap more, increasing bulk, thereby increasing the rigidity of the surface protective material and improving handleability. When the reinforcing fibers constituting the nonwoven fabric substrate are in the form of short fibers, the fiber length is preferably 2 to 30 mm, more preferably 2 to 15 mm, and even more preferably 4 mm to 13 mm. A fiber length of 2 mm or more can reduce the number of reinforcing fibers per unit weight of the nonwoven fabric, which is preferable because the effect of springback is limited even if it occurs. A fiber length of 30 mm or less increases the rigidity of the surface protective material and achieves better handleability.

[0040] The fiber diameter of the reinforcing fibers constituting the nonwoven fabric substrate used in the present invention is preferably 3 to 20 μm, more preferably 3 to 12 μm, even more preferably 3 to 8 μm, and even more preferably 5 to 8 μm. When the fiber diameter of the reinforcing fibers is 3 μm or more, the rigidity of the surface protective material is increased, achieving better handleability. When the fiber diameter is 20 μm or less, the rigidity of the reinforcing fibers is low, so springback is small and pinholes can be more easily suppressed.

[0041] When it is necessary to measure the fiber length and fiber diameter (diameter), the nonwoven fabric substrate is observed with an optical microscope, 20 reinforcing fibers are arbitrarily selected from the observation image, the fiber length and fiber diameter of each reinforcing fiber are measured, and the average is calculated. As the nonwoven fabric substrate used for the measurement, as described above, one extracted by the method using the above solvent when determining the basis weight of the nonwoven fabric substrate may be used.

[0042] Examples of reinforcing fibers constituting the nonwoven fabric substrate used in the present invention include carbon fibers, boron fibers, high-strength polyethylene fibers, tungsten carbide fibers, PBO fibers, polyester fibers, vinylon fibers, aramid fibers, and glass fibers, and these may be used alone or in combination of two or more.

[0043] The tensile modulus of the reinforcing fibers constituting the nonwoven fabric substrate used in the present invention is preferably 60 to 350 GPa, more preferably 60 to 150 GPa, and even more preferably 60 to 100 GPa. When the tensile modulus is 60 GPa or more, the rigidity of the surface protective material is increased, achieving better handleability. When the tensile modulus is 350 GPa or less, the reinforcing fiber does not have a high modulus of elasticity, so springback is small and pinholes can be more easily suppressed. Specifically, glass fibers are preferably used as reinforcing fibers having a tensile modulus within this range.

[0044] The tensile modulus can be measured by a method according to JIS R 7606:2000 (calculation method: Method A), and the average value measured for 20 reinforcing fibers is used.

[0045] The tensile modulus may be measured by extracting reinforcing fibers from the nonwoven fabric substrate extracted by the method described above for measuring the basis weight of the substrate in the surface protective material. Furthermore, when measuring the tensile modulus, if the fiber length of the reinforcing fibers constituting the nonwoven fabric substrate is shorter than 25 mm, the sample length may be changed accordingly.

[0046] The gap of the nonwoven fabric substrate is preferably 3 to 35%, more preferably 3 to 20%, even more preferably 3 to 13%, and even more preferably 3 to 10%. When the gap of the nonwoven fabric substrate is 3% or more, the drapeability of the surface protective material is improved and handling is favorable. When the gap of the nonwoven fabric substrate is 35% or less, the degree of impregnation in the surface protective material is low and the difference in the degree of exposure of the nonwoven fabric substrate on both sides is small, making it easier to suppress pinholes.

[0047] The voids of the nonwoven fabric substrate can be determined by observation with an optical microscope, and can be measured using, for example, a VHX-5000 (manufactured by Keyence Corporation). Details of other measurement methods are as described in the examples, but different methods may be used as long as they can obtain the same results.

[0048] The orientation distribution (represented as f) of the reinforcing fibers constituting the nonwoven fabric substrate is preferably 0.300 to 0.637, more preferably 0.580 to 0.636, even more preferably 0.610 to 0.636, and even more preferably 0.630 to 0.636. When the orientation distribution of the reinforcing fibers constituting the nonwoven fabric substrate is 0.300 or more, the nonwoven fabric substrate is bulky, the degree of impregnation in the surface protective material is low, and the difference in the degree of exposure of the nonwoven fabric substrate on both sides is small, making it easier to suppress the pinholes. Furthermore, the reinforcing fibers of the nonwoven fabric substrate are more uniformly dispersed, and the density of the reinforcing fibers is reduced, making it possible to further reduce the size of the pinholes that occur. When the orientation distribution of the reinforcing fibers constituting the nonwoven fabric substrate is 0.637 or less, the drapeability of the surface protective material is improved and handling is better.

[0049] The orientation distribution of the reinforcing fibers constituting the nonwoven fabric substrate is an index of the randomness of the reinforcing fibers in the nonwoven fabric substrate, and can be expressed by the following formula 1.

[0050]

[0051] Here, n is the number of reinforcing fibers in the nonwoven fabric substrate, θ is the angle between an arbitrary baseline and a reinforcing fiber in the nonwoven fabric substrate, and θi and θj are the angles between the baseline and the i-th reinforcing fiber and the j-th reinforcing fiber, respectively.

[0052] The orientation distribution f of the reinforcing fibers constituting the nonwoven fabric substrate can be determined by observation with an optical microscope, and can be measured using, for example, a VHX-5000 (manufactured by Keyence Corporation). Details of other measurement methods are as described in the examples, but different methods may be used as long as the same results can be obtained. "Epoxy Resin Composition" Each component of the epoxy resin composition used in the present invention will be described in detail. In the present invention, the epoxy resin composition refers to a mixture containing an epoxy resin, a curing agent, and other components.

[0053] In the method for producing a prepreg according to the present invention, the method for handling the epoxy resin composition is not particularly limited. For example, the epoxy resin composition can be handled as it is, or can be handled after being dissolved in a solvent to reduce the viscosity, or can be handled after partially promoting a reaction by heat, light, or the like to increase the viscosity of the epoxy resin composition.

[0054] The epoxy resin composition used in the present invention preferably exhibits high resistance to springback. The present inventors have found that the shear stress required for an epoxy resin composition to start flowing after being left to stand serves as an index of resistance to springback, and that the Casson yield value at 74°C shown below can be used as an index of the shear stress required for the composition to start flowing.

[0055] The Casson yield value refers to a characteristic value used in the Casson equation (the following equation), which is an equation that theoretically deals with the rheological characteristics of a suspension in which solid particles are dispersed in a Newtonian fluid.

[0056] τ ０．５ = τ ｙ ０．５ +η∞ ０．５ ×γ ０．５ where τ is shear stress (Pa), γ is shear rate (s －１ ), η ∞ :Casson viscosity (Pa・s), τ ｙ : Casson yield value (Pa). In the present invention, the Casson yield value is evaluated at a temperature of 74°C.

[0057] The Casson yield value at 74°C of the epoxy resin composition used in the present invention is preferably 70 to 1000 Pa, more preferably 120 to 1000 Pa, even more preferably 210 to 1000 Pa, and even more preferably 210 to 750 Pa. When the Casson yield value is 70 Pa or more, the resistance to springback is higher and the occurrence of pinholes can be more easily suppressed. On the other hand, when the Casson yield value is 1000 Pa or less, the processability when forming the epoxy resin composition into a film is superior.

[0058] The Casson yield value can be evaluated by dynamic viscoelasticity measurement, for example, using a dynamic viscoelasticity device ARES-G2 (manufactured by TA Instruments Co., Ltd.) Details of other measurement methods are as described in the examples, but different methods may be used as long as they can obtain the same results.

[0059] For evaluation of the Casson yield value, the epoxy resin composition before being made into a surface protective material may be used, or the epoxy resin composition may be extracted from the surface protective material by sandwiching the surface protective material between two sheets of release paper and applying heat and pressure with an iron to partially separate the epoxy resin composition from the nonwoven fabric substrate and transfer it to the release paper, and then removing the release paper. "Component [A]" The epoxy resin composition used in the present invention contains a non-aromatic epoxy resin (component [A]).

[0060] When the epoxy resin composition contains a non-aromatic epoxy resin, light resistance is imparted to the surface protective material after curing.

[0061] The viscosity of the non-aromatic epoxy resin is preferably 0.1 to 1,000,000 Pa·s at 25°C, more preferably 0.15 to 1,000,000 Pa·s, and even more preferably 0.20 to 1,000,000 Pa·s. When the viscosity is 0.1 Pa·s or higher, the resistance to springback is higher, and pinholes can be more easily suppressed. When the viscosity is 1,000,000 Pa·s or lower, the epoxy resin composition can be more easily formed into a film. The viscosity of the non-aromatic epoxy resin can be measured at 25°C in accordance with JIS K 5600-2-3:2014.

[0062] When the total amount of epoxy resins in the epoxy resin composition is taken as 100 parts by mass, the amount of the non-aromatic epoxy resin is preferably 90 parts by mass or more, more preferably 95 parts by mass or more, and even more preferably 100 parts by mass. When the amount of the non-aromatic epoxy resin is 90 parts by mass or more, good light resistance can be imparted to the surface protective material, and a surface-protected fiber-reinforced composite material excellent in appearance and light resistance can be obtained.

[0063] Examples of non-aromatic epoxy resins include aliphatic epoxy resins and alicyclic epoxy resins.

[0064] Aliphatic epoxy resins are epoxy resins that have an aliphatic skeleton that does not contain a cyclic structure and that do not contain aromatic rings. Alicyclic epoxy resins are epoxy resins that have a cyclic aliphatic skeleton and that do not contain aromatic rings, and are classified into compounds that contain a structure in which at least one group selected from epoxy groups, glycidyl groups, glycidyloxy groups, and glycidyl ester groups is directly bonded to a cycloalkane (abbreviated as epoxidized cycloalkane), and compounds that contain a 1,2-epoxycycloalkane structure.

[0065] Examples of such epoxidized cycloalkanes are represented by the following chemical structures:

[0066]

[0067] An example of an epoxidized cycloalkane containing an epoxy group is 2,2-bis(hydroxymethyl)-1-butanol to 1,2-epoxy-4-(2-oxiranyl)cyclohexane adduct (the above-mentioned formula (1)). An example of a commercially available product is EHPE3150 (manufactured by Daicel Chemical Industries, Ltd.). Furthermore, an example of an epoxidized cycloalkane containing a glycidyloxy group is diglycidyl ether of 2,2-bis(4-hydroxycyclohexyl)propane (general name: hydrogenated bisphenol A epoxy resin) (the above-mentioned formula (2)) or long-chain hydrogenated bisphenol A epoxy resin (the above-mentioned formula (3)). Examples of commercially available products include ST-3000, ST-4000, ST-6100 (manufactured by Nippon Steel Chemical & Material Co., Ltd.), YX8000 (manufactured by Mitsubishi Chemical Corporation), and "EPALLOY (registered trademark)" 5000 (manufactured by HUNTSMAN). An example of an epoxidized cycloalkane containing a glycidyl ester group is hexahydrophthalic acid diglycidyl ester (the above-mentioned formula (4)) having the following chemical structure. Commercially available examples include EPOXY RESIN EPOXMK SHIRIES R540 (manufactured by Air Water Inc.).

[0068] Examples of compounds containing the 1,2-epoxycycloalkane structure are represented by the following chemical structures:

[0069]

[0070]

[0071] Among compounds containing a 1,2-epoxycycloalkane structure, examples of compounds containing two 1,2-epoxycyclohexanes include (3',4'-epoxycyclohexane)methyl 3,4-epoxycyclohexanecarboxylate (the aforementioned formula (5)), epsilon-caprolactone-modified 3,4-epoxycyclohexylmethyl 3',4'-epoxycyclohexanecarboxylate (the aforementioned formula (6)), and bis(3,4-epoxycyclohexylmethyl)adipate (the aforementioned formula (7)). Examples of commercially available products include "Celloxide (registered trademark)" 2021P and 2081 (manufactured by Daicel Chemical Industries, Ltd.), Syna-Epoxy 28, 21, 06E, and 10 (manufactured by SYNASIA), UviCure S128 (manufactured by Arkema K.K.), and TTA21 (Sun Chemical Co., Ltd.). Furthermore, among compounds containing a 1,2-epoxycycloalkane structure, an example of a compound containing four 1,2-epoxycyclohexanes is epoxidized butanetetracarboxylic acid tetrakis-(3-cyclohexenylmethyl)-modified epsilon-caprolactone-caprolactone (the aforementioned formula (8)). An example of a commercially available product is "Epolead (registered trademark)" GT401 (manufactured by Daicel Chemical Industries, Ltd.). Furthermore, among compounds containing a 1,2-epoxycycloalkane structure, a compound having formed a condensed ring containing one or more 1,2-epoxycycloalkane structures is exemplified. Examples of these compounds include tetrahydroindene-type diepoxides and tricyclopentadiene-type diepoxides. Examples of commercially available products include "Epocalic (registered trademark)" THI-DE and DE-102 (manufactured by ENEOS Corporation). Furthermore, among compounds forming a fused ring containing one or more 1,2-epoxycycloalkane structures, an example of a compound containing two 1,2-cyclopentanes is pentacyclopentadecadiene diepoxide. An example of a commercially available product is "Epocalic (registered trademark)" DE-103 (manufactured by ENEOS Corporation). "Component [B]" The epoxy resin composition used in the present invention contains a thixotropic agent (component [B]).

[0072] By including a thixotropic agent in the epoxy resin composition, the cohesive strength of the epoxy resin composition is increased, and the epoxy resin composition exhibits high resistance to springback, thereby suppressing the occurrence of pinholes.

[0073] A thixotropic agent refers to a particulate material that imparts thixotropy to an epoxy resin composition. Thixotropy refers to a reversible property in which viscosity decreases under shear stress and returns to its original state when left standing. Here, thixotropy can be evaluated by the method described in JIS R1665:2005. The higher the thixotropy, the higher the Casson yield value.

[0074] To improve the thixotropy of an epoxy resin composition, it is necessary to utilize the hydrogen bonds and electrostatic interactions that occur between the fine particles of the thixotropic agent, and for this reason, the specific surface area of ​​the thixotropic agent is important. Specifically, in the epoxy resin composition used in the present invention, which requires a non-aromatic epoxy resin, the specific surface area of ​​the thixotropic agent is 60 to 300 m. ２ / g, and 65 to 200m ２ / g, and more preferably 70 to 150m ２ It is more preferable that the specific surface area of ​​the thixotropic agent is 60 m / g. ２ When the specific surface area of ​​the thixotropic agent is 300 m / g or more, the interaction within the thixotropic agent increases, so that the cohesive force of the epoxy resin composition becomes higher, and the pinholes can be more easily suppressed. ２ When the specific surface area of ​​the thixotropic agent is 1 / g or less, the amount of coarse aggregates of the thixotropic agent in the epoxy resin composition is small, and the thixotropic agent can be easily dispersed well by stirring or passing through a triple roll mill, thereby further enhancing the effect of the thixotropic agent. The specific surface area of ​​the thixotropic agent can be measured by JIS Z 8830:2013 (BET method).

[0075] The thixotropic agent is preferably contained in an amount of 3 to 14 parts by mass, more preferably 3 to 10 parts by mass, even more preferably 3 to 8 parts by mass, and even more preferably 4 to 8 parts by mass, relative to 100 parts by mass of the total epoxy resin in the epoxy resin composition. When the amount of the thixotropic agent is 3 parts by mass or more, the thixotropy of the epoxy resin composition can be further improved. Furthermore, when the amount of the thixotropic agent is 14 parts by mass or less, the thixotropic agent is well dispersed in the epoxy resin composition, and the effect per unit amount of the thixotropic agent can be further increased.

[0076] Examples of the thixotropic agent include silica containing silicon dioxide, synthetic hectorite, clay minerals, bentonite, and a mixture of organically modified bentonite.

[0077] Examples of commercially available products include "Aerosil (registered trademark)" 50, 90G, 130, 150, 200, 300, 380, and RY200S (manufactured by EVONIK), "Aeroxide (registered trademark)" AluC, Alu65, Alu130, and TiO2T805 (manufactured by Nippon Aerosil Co., Ltd.), "Leoseal (registered trademark)" PM-20L, HM-20L, and DM-20S (manufactured by Tokuyama Corporation), and "CAB-O-SIL (registered trademark)" TS610, TS710, TS720, and TS5780 (manufactured by CAB OT Co., Ltd.), "OPTIGEL (registered trademark)" WX, "OPTIBENT (registered trademark)" 616, "GARAMITE (registered trademark)" 1958, 7305, "LAPONITE (registered trademark)" S-482, "TIXOGEL (registered trademark)" MP, VP, "CRAYTONE (registered trademark)" 40, "CLOISITE (registered trademark)" 20A (manufactured by BYK Corporation), "Somasif (registered trademark)" ME-100, Micromica MK (manufactured by Katakura Co-op Agri Co., Ltd.), and the like.

[0078] The thixotropic agent may be used after surface treatment. Examples of surface treatment agents used for the thixotropic agent include dimethyldichlorosilane, hexamethyldisilazane, octylsilane, and dimethylpolysiloxane. Fumed silica with dimethylpolysiloxane applied as a surface treatment agent is preferred because it has good dispersibility in the epoxy resin composition used in the present invention and imparts high thixotropy. "Component [C]" The epoxy resin composition used in the present invention contains a curing agent (component [C]). The type of curing agent is not particularly limited, and examples include amine-based curing agents, anionic curing agents, cationic curing agents, and acid anhydride curing agents.

[0079] Examples of amine-based curing agents include dicyandiamide, diaminodicyclohexylmethane, and 1,3-BAC. Commercially available products include "jER Cure (registered trademark)" DICY7 (manufactured by Mitsubishi Chemical Corporation). When dicyandiamide is used as the curing agent, a curing accelerator such as a urea compound can be used in combination.

[0080] Examples of anionic curing agents include imidazoles and urea compounds, and commercially available products thereof include Curesol 1,2DMZ (manufactured by Shikoku Chemical Industry Co., Ltd.), DCMU99 (manufactured by Hodogaya Chemical Co., Ltd.), and "Omicure (registered trademark)" 24, U-24M, and U-52M (manufactured by CVC Thermoset Specialties).

[0081] Examples of cationic curing agents include cations such as Bronsted acids, Lewis acids, and carbocations, as well as precursors thereof. Among these, onium salts, which can serve as precursors of acids or cations, are preferred because they can impart low-temperature curing properties to epoxy resin compositions and have excellent stability at the process temperatures used to form epoxy resin compositions into films. Examples of onium salts include ammonium salts, phosphonium salts, sulfonium salts, and iodonium salts. Specific examples include 1-naphthylmethylmethyl p-hydroxyphenylsulfonium hexafluoroantimonate, 2-methylbenzylmethyl p-hydroxyphenylsulfonium hexafluoroantimonate, benzylmethyl p-hydroxyphenylsulfonium hexafluoroantimonate, dimethyl-p-acetoxyphenylsulfonium hexafluoroantimonate, and diaryliodonium salts. Commercially available products include "ADEKAOPTON (registered trademark)" CP-77 (manufactured by ADEKA Corporation), "SAN-AID (registered trademark)" SI-60, "SAN-AID (registered trademark)" SI-80, "SAN-AID (registered trademark)" SI-100, "SAN-AID (registered trademark)" SI-150, "SAN-AID (registered trademark)" SI-B4 (manufactured by Sanshin Chemical Industry Co., Ltd.), TA-100, IK-1PC (80) (manufactured by San-Apro Ltd.), and "K-Pure (registered trademark)" CXC-1612 (manufactured by King Industries). Of these, sulfonium salts are preferred because they can impart low-temperature curing properties to the epoxy resin composition and are particularly excellent in low-temperature curing properties and stability at the process temperatures for forming the epoxy resin composition into a film.

[0082] Examples of acid anhydride curing agents include hexahydrophthalic anhydride, and examples of commercially available products include "RIKACID (registered trademark)" HH, TH, and HNA-100 (manufactured by New Japan Chemical Co., Ltd.). When an acid anhydride is used as the curing agent, it can be used in combination with a curing accelerator such as triphenylphosphine.

[0083] The reactivity can be controlled by appropriately combining the component [A] and the component [C]. The curing initiation temperature can be controlled by combining one or more components [A] with one or more components [C].

[0084] When an alicyclic epoxy resin containing a 1,2-epoxycycloalkane structure is used as the component [A], it is preferable to use a cationic curing agent as the component [C], since this can impart low-temperature curing properties to the epoxy resin composition and also reduces the flow index.

[0085] When an aliphatic epoxy resin or an alicyclic epoxy resin corresponding to an epoxidized cycloalkane is used as the component [A], it is preferable to use an amine-based curing agent or an anionic curing agent as the component [C], since this can impart low-temperature curing properties to the epoxy resin composition.

[0086] When the epoxy resin composition contained in the composite material precursor contains an aromatic epoxy resin, if the surface protective material used in the present invention is placed on the surface of the composite material precursor and they are thermally cured together, the aromatic epoxy resin may mix with the surface protective material, resulting in a decrease in the light resistance of the surface-protected fiber-reinforced composite material. When the epoxy resin composition used in the present invention is cured in a low temperature range, this mixing is suppressed, making it possible to form a surface-protected fiber-reinforced composite material with high light resistance. "Component [D]" The epoxy resin composition used in the present invention preferably further contains a non-aromatic thermoplastic resin (component [D]).

[0087] By including such a non-aromatic thermoplastic resin, the cohesive strength of the epoxy resin composition can be increased, and the composition can exhibit high resistance to springback. As a result, the pinholes can be more easily suppressed while maintaining good light resistance.

[0088] When the epoxy resin composition used in the present invention further contains a non-aromatic thermoplastic resin, the amount of the non-aromatic thermoplastic resin is preferably 20 to 70 parts by mass, more preferably 35 to 70 parts by mass, and even more preferably 35 to 60 parts by mass, relative to 100 parts by mass of all epoxy resins in the epoxy resin composition. When the amount of the non-aromatic thermoplastic resin is 20 parts by mass or more, the surface protective material is easy to handle and pinholes can be more easily prevented. Furthermore, when the amount is 70 parts by mass or less, the ease of forming a resin film is excellent, which is preferable.

[0089] The number average molecular weight of the non-aromatic thermoplastic resin is preferably 10,000 to 60,000 g / mol, more preferably 16,000 to 50,000 g / mol, and even more preferably 16,000 to 40,000 g / mol. When the number average molecular weight is 60,000 g / mol or less, the surface protection material becomes easier to handle. When the number average molecular weight is 10,000 g / mol or more, the cohesive strength of the epoxy resin composition is increased, resulting in higher resistance to springback, thereby further suppressing the occurrence of pinholes. Here, the number average molecular weight refers to the number average molecular weight in terms of polystyrene measured by gel permeation chromatography.

[0090] Examples of non-aromatic thermoplastic resins include polyvinyl alcohol and acetalized polyvinyl alcohol compounds, such as polyvinyl acetal, polyvinyl formal, polyvinyl acetoacetal, and polyvinyl butyral. Other examples of non-aromatic thermoplastic resins include polyvinyl acetate, hydrogenated bisphenol A-pentaerythritol phosphite polymer, hydrogenated terpene, and hydrogenated terpene phenol.

[0091] Examples of commercially available non-aromatic thermoplastic resins include "J-POVAL (registered trademark)" (manufactured by Nippon Vinyl Acetate & Poval Co., Ltd.), "S-LEC (registered trademark)" (manufactured by Sekisui Chemical Co., Ltd.), "Ultrasene (registered trademark)" (manufactured by Tosoh Corporation), "JPH-3800" (manufactured by Johoku Chemical Industry Co., Ltd.), and "YS Polystar UH130" (manufactured by Yasuhara Chemical Co., Ltd.).

[0092] These non-aromatic thermoplastic resins are preferably soluble in the epoxy resin of component [A]. Here, "soluble" means that when at least 10 parts by mass of thermoplastic resin powder is added to 100 parts by mass of the non-aromatic epoxy resin of component [A] and kneaded at 120°C for 1 hour, a weight loss of the thermoplastic resin powder is observed compared to the start of kneading. "Weight loss" means that the powder becomes so small that it is optically unobservable, or that when the remaining powder is recovered, a weight loss of 10% or more is observed compared to the start of kneading.

[0093] From the viewpoint of dissolving the thermoplastic resin in a non-aromatic epoxy resin, it is preferable that the thermoplastic resin powder has an average particle size of 100 μm or less as determined by a laser diffraction method, for reasons such as preventing aggregation during storage and facilitating stirring into the epoxy resin.

[0094] Polyvinyl acetals, which have high solubility in non-aromatic epoxy resins, are preferred in that the viscosity of the epoxy resin composition can be easily adjusted. "Component [E]" The epoxy resin composition used in the present invention preferably contains a pigment (component [E]).

[0095] When the epoxy resin composition used in the present invention contains a pigment, the blending amount of the pigment is preferably 20 to 60 parts by mass, more preferably 30 to 60 parts by mass, and even more preferably 30 to 50 parts by mass, relative to 100 parts by mass of the total epoxy resin in the epoxy resin composition. An amount of the pigment of 20 parts by mass or more is preferred because the surface protective material has excellent light-blocking properties. The light-blocking properties of the surface protective material can suppress the penetration of UV into the fiber-reinforced composite material, thereby enabling the production of a surface-protected fiber-reinforced composite material with even better appearance and light resistance. An amount of the pigment of 60 parts by mass or less is preferred because it does not make it difficult to form the epoxy resin composition into a film.

[0096] Examples of pigments include barium sulfate, zinc sulfide, titanium oxide, molybdenum red, cadmium red, chromium oxide, titanium yellow, cobalt green, cobalt blue, ultramarine, barium titanate, carbon black, iron oxide, red phosphorus, and copper chromate.

[0097] "Other Additives" The epoxy resin composition used in the present invention may contain additives as needed. The type of additive is not particularly limited, but may include additives such as curing accelerators, curing inhibitors, rubbers, flame retardants, light stabilizers, antioxidants, and defoamers.

[0098] "Method for producing surface protective material" There are no particular limitations on the method for producing the surface protective material of the present invention, but a method is used in which the epoxy resin composition is processed into a resin film, and the resin film is then superimposed on a nonwoven fabric substrate and impregnated by heating and / or compression. In this case, the impregnation may be performed by disposing the resin film on both sides of the nonwoven fabric substrate, or by disposing the resin film on only one side of the nonwoven fabric substrate. Here, the process of coating the epoxy resin composition on a support such as release paper or thermoplastic film is referred to as film formation, and the material obtained by film formation is referred to as a resin film. There are no particular limitations on the method for film formation, but examples include the common hot melt method and wet method. There are also no particular limitations on the method for using the resin film. It may be used as is, or, for example, it may be used after proceeding with curing and adjusting the viscosity.

[0099] The surface protective material can also be produced by directly applying the epoxy resin composition to a substrate and impregnating it.

[0100] The substrate of the surface protective material of the present invention may be impregnated with the epoxy resin composition from both the front and back surfaces of the substrate, or from only one surface of the substrate.

[0101] "Method of Using Surface Protective Material" There are no particular limitations on the method of using the surface protective material of the present invention. The sheet-like surface protective material may be used as is, or may be used after, for example, allowing curing to proceed and adjusting the viscosity.

[0102] As a method for using the surface protective material of the present invention, for example, the surface protective material of the present invention can be attached to the outermost surface on one or both sides of a fiber-reinforced composite material precursor, which is a single layer of prepreg or a laminate of multiple prepreg layers, to form a surface-protected fiber-reinforced composite material precursor, which can then be cured to obtain a surface-protected fiber-reinforced composite material. Alternatively, the surface protective material alone can be used as a single layer or as a laminate of multiple layers, which can then be cured to obtain a molded product.

[0103] The surface protective material of the present invention can be used in combination with a composite material precursor, a fiber-reinforced composite material, or other materials. Specifically, it can be used as an adhesive layer by being disposed between the same or different materials selected from a composite material precursor, a fiber-reinforced composite material, a metal, etc.

[0104] "Surface-protected fiber-reinforced composite material" A surface-protected fiber-reinforced composite material produced using the surface-protective material of the present invention is a highly light-resistant material, and contributes to improving the service life of wind turbine blades, automobile exterior panels, laptop computer housings, and particularly aircraft components.

[0105] The present invention will be described in more detail below with reference to examples, although the scope of the present invention is not limited to these examples.

[0106] <Materials used in Examples and Comparative Examples> (1) Component [A] Non-aromatic epoxy resin (3',4'-epoxycyclohexane)methyl 3,4-epoxycyclohexanecarboxylate ("Celloxide (registered trademark)" 2021P, manufactured by Daicel Corporation, epoxy equivalent: 136 (g / eq.), liquid at room temperature) Diglycidyl ether of 2,2-bis(4-hydroxycyclohexyl)propane ("EPALLOY (registered trademark)" 5000, manufactured by HUNTSMAN, epoxy equivalent: 210 (g / eq.), liquid at room temperature) (2) Component [B] Thixotropic agent Fumed silica ("AEROSIL (registered trademark)" RY200S, manufactured by Nippon Aerosil Co., Ltd., specific surface area 80 m ２ / g) Fumed silica ("Leoseal (registered trademark)" DM-20S, manufactured by Tokuyama Corporation, specific surface area 180 m ２ / g) Fumed silica ("Leoseal (registered trademark)" PM-20L, manufactured by Tokuyama Corporation, specific surface area 100 m ２ / g) Fumed silica ("CAB-O-SIL (registered trademark)" TS710, manufactured by CABOT Corporation, specific surface area 100 m ２ / g) Fumed silica ("CAB-O-SIL (registered trademark)" TS720, manufactured by CABOT Corporation, specific surface area 120 m ２ / g) (3) Component [C] Curing Agent Benzylmethyl p-hydroxyphenylsulfonium hexafluoroantimonate ("Sanaide (registered trademark)" SI-100, manufactured by Sanshin Chemical Industry Co., Ltd.) Dicyandiamide ("jER Cure (registered trademark)" DICY7 (manufactured by Mitsubishi Chemical Corporation)) (4) Component [D] Non-aromatic Thermoplastic Resin Polyvinyl formal ("Vinylec (registered trademark)" K, manufactured by JNC Corporation, number average molecular weight 40,000 to 54,000 g / mol) Polyvinyl acetoacetal ("S-LEC (registered trademark)" KS-10, manufactured by Sekisui Chemical Co., Ltd., number average molecular weight 17,000 g / mol) (5) Component [E] Pigment Titanium oxide (rutile type) ("Ti-Pure (registered trademark)" R-960, manufactured by Chemours Inc., average particle size 0.5 μm) (6) Nonwoven fabric substrate: Grabestos EVP-017 (glass fiber nonwoven fabric, polyvinyl alcohol (PVA) binder used) (manufactured by Olivest Co., Ltd., fiber basis weight 17 g / m ２ , fiber diameter 6 μm, fiber length 6 mm) Grabestos EVP-020 (glass fiber nonwoven fabric, polyvinyl alcohol (PVA) binder used) (manufactured by Olivest Co., Ltd., fiber basis weight 20 g / m ２ , fiber diameter 6 μm, fiber length 6 mm) Grabestos EVP-023 (glass fiber nonwoven fabric, polyvinyl alcohol (PVA) binder used) (manufactured by Olivest Co., Ltd., fiber basis weight 23 g / m ２ , fiber diameter 6 μm, fiber length 6 mm) Optiveil 20103A (glass fiber nonwoven fabric, PVA binder used) (tfp, fiber basis weight 17 g / m ２ , fiber diameter 11 μm, fiber length 15 mm) Optiveil 20254A (PET fiber nonwoven fabric, polyester binder used) (tfp, fiber basis weight 12 g / m ２, fiber diameter 6 μm, fiber length 5 mm) (7) Prepreg (target of surface protection) T800S / 3900-2B (continuous fiber) prepreg (manufactured by Toray Industries, Inc.).

[0107] (8) Curing accelerator: Toluene bis(dimethylurea) "Omicure (registered trademark)" 24 (manufactured by CVC Thermoset Specialties) <Methods for preparing epoxy resin compositions, resin films, and surface protective materials> The epoxy resin compositions, resin films, and surface protective materials of each of the examples and comparative examples were prepared by the following methods.

[0108] (1) Preparation of Epoxy Resin Composition For each example, 20 parts by mass of the component [A], the entire amount of the component [C], and the entire amount of the component [E] were mixed together in the composition shown in the table, and then mixed using a triple roll mill to obtain a precursor in which powders were mixed.

[0109] Separately, the remaining 80 parts by mass of component [A] and the entire amount of component [D] were charged into a mixer and kneaded by heating at 120°C for 1 hour to dissolve the non-aromatic thermoplastic resin in the non-aromatic epoxy resin. Next, while continuing kneading, the temperature was lowered to 60°C or lower, the precursor prepared as above was added and stirred and mixed, and then component [B] and, if necessary, a curing accelerator were added and stirred and mixed to obtain an epoxy resin composition.

[0110] (2) Preparation of Resin Film The epoxy resin composition prepared in (1) was applied to release paper using a knife coater to achieve the target basis weight, to prepare a resin film. The quality of the prepared resin film was confirmed visually. Examples of cases where the quality was poor include the following: a. There were areas on the release paper where the epoxy resin composition was not applied. b. The epoxy resin composition did not pass between the rolls of the knife coater.

[0111] The resin film being of good quality means that it does not fall into any of the above a to b.

[0112] (3) Preparation of Surface Protective Materials One resin film prepared in (2) was placed on one side of a nonwoven fabric substrate, and then both sides were sandwiched between release papers. A vacuum (76 cmHg) was applied under the impregnation conditions shown in the table for the time indicated for each example, thereby impregnating the epoxy resin composition to obtain a surface protective material. In the obtained surface protective material, a very thin resin layer containing the epoxy resin composition was laminated on one side of the nonwoven fabric substrate to form a resin surface, and a portion of the epoxy resin composition in the resin layer was impregnated into the nonwoven fabric substrate. The epoxy resin composition did not completely impregnate the opposite side of the nonwoven fabric substrate, or even if it did, it was not impregnated in a sufficient amount. That is, the side on which the resin film was laminated had a greater amount of impregnated epoxy resin composition than the opposite fiber side.

[0113] (4) Preparation of Surface-Protected Fiber-Reinforced Composite Material Eight sheets of the prepreg described in (7) of <Materials Used in Examples and Comparative Examples> were stacked in a quasi-isotropic manner (lamination structure: [+45° / 0° / -45° / 90°]). ｓ ) to prepare a composite material precursor, to which the resin surface of the surface protection material prepared in (3) was attached on the outermost surface. In this state, the composite material was cured in an autoclave under conditions of 6 atmospheres, 180°C, 2 hours, and a temperature increase rate of 1.7°C / min, to obtain a surface-protected fiber-reinforced composite material.

[0114] <Evaluation Methods for Epoxy Resin Composition, Resin Film, and Surface Protective Material> Each material was evaluated by the following method. Unless otherwise noted, these evaluations were performed in an environment of 23°C and 50% relative humidity, with n=1.

[0115] (1) Casson Yield Value of Epoxy Resin Composition The epoxy resin composition was extracted from the prepared surface protective material, and the Casson yield value was evaluated.

[0116] The surface protective material was sandwiched between two sheets of release paper, and heat and pressure were applied with an iron to partially separate the epoxy resin composition contained in the surface protective material from the nonwoven fabric substrate. The epoxy resin composition attached to the release paper was sampled, and its Casson yield value was measured using an ARES-G2 dynamic viscoelasticity analyzer (manufactured by TA Instruments). The measurement temperature was 74°C, and flat parallel plates with a diameter of 25 mm were used as the upper and lower measuring jigs. The epoxy resin composition was set between the upper and lower jigs so that the distance between the upper and lower jigs was 1 mm, and then measurement was performed in flow ramp mode. The shear rate was 0.01 to 100 s －１ The Casson yield value was set to a range of 0.01 to 49 s －１ The shear rate was calculated according to Equation 1 in the range of τ ０．５ , the horizontal axis is γ ０．５ This is because when the measurement results are plotted, they become linear within the above range.

[0117] (2) Evaluation of Pinholes After Storage of Surface Protective Material The surface protective material was cut into a 10 cm x 10 cm square sample, which was sandwiched between two sheets of release paper and stored at 23°C for 7 days, after which the release paper was peeled off. Next, in a state where the area where pinholes occurred and the surface protective material area were easily distinguished (the surface protective material was attached to drawing paper of a different color from the surface protective material), the sample was observed at a magnification of 20 times using an optical microscope (VHX-5000 (manufactured by Keyence Corporation)), and the size of the pinholes penetrating the front and back of the surface protective material was evaluated. The surface protective material (100 cm ２ The hole with the largest diameter on the surface was extracted from the sample, and this diameter was taken as the maximum diameter of the pinhole. If the shape of the pinhole was not a perfect circle, the point with the longest distance between two points in the hole was taken as the maximum diameter of each sample. The maximum diameter of the pinhole was determined by measuring the maximum diameter of the pinhole for each of five pieces of surface protection material cut into a 10 cm x 10 cm square at random positions, and the average value was used as the maximum diameter of the pinhole.

[0118] (3) Impregnation Degree of Surface Protective Material (Water Uptake Test) The surface protective material was cut into a 10 cm x 10 cm square to prepare a sample. If the surface protective material was attached to release paper or the like, the release paper was removed. The mass W1 (unit: g) of this surface protective material was measured. Next, the surface protective material was positioned between two PTFE-backed aluminum plates (PTFE-backed plate assembly), and one direction of the 10 cm long side of the sample was protruded 15 mm from one end of the PTFE-backed plate assembly. A clamp was placed at the opposite end, and a portion of the 15 mm protruding portion, up to 5 mm from the tip, was immersed in water at 23°C. After immersion for 5 minutes, the surface protective material was removed from the water, and the surface water was removed with blotting paper. The mass W2 (unit: g) of the surface protective material was then measured. The water uptake rate (WPU (unit: %)) of each sample was calculated from W1 and W2 using the following formula: WPU (%) = [(W2 - W1) / W1] × 100 WPU was determined as the average value of the values ​​measured for each of five pieces of surface protection material that were cut into 10 cm × 10 cm squares at arbitrarily selected positions and calculated using the above formula.

[0119] (4) Surface Tack of Surface Protective Material The tack of the surface protective material was measured by a rolling ball tack test. The method was as follows:

[0120] Double-sided tape (50 mm wide, manufactured by Nitto Denko) was attached to a workbench that was confirmed to be level, and a surface protection material test piece cut to a length of 30 cm (in the direction of rolling the ball) and an arbitrary predetermined width was attached to the double-sided tape so that the tack measurement surface (resin surface or fiber surface) was facing up. A line was drawn 3 cm from one end of the longitudinal direction of the surface protection material, and masking tape was attached to the surface protection material so as to cover the area from the end to the line. A PI-1202 Rolling Ball Tack Tester (manufactured by Tester Sangyo Co., Ltd., inclined surface 165 mm, angle 21.5°, steel ball 7 / 16 inch, compliant with ASTM D3121:1999) was placed on the masking tape, and the tip of the tester was aligned with the line. The ball stopper of the tester was slid, and the ball was rolled on the tack measurement surface of the surface protection material. The distance from the tip of the tester to the center of the rolling ball was measured, and the tackiness was evaluated by measuring the distance traveled by the ball rolling on the surface protective material, which was recorded as "ball travel distance on the fiber surface" or "ball travel distance on the resin surface" in the table. The shorter the ball travel distance, the higher the tackiness of the surface of the surface protective material. Note that if the ball passed over the surface protective material (if the distance exceeded 270 mm), it was deemed that there was no tackiness. Each measurement was performed five times, and the average was taken as the measured value. However, if the ball passed over the surface protective material even once during the five measurements, it was deemed that there was no tackiness.

[0121] (5) Handleability of Surface Protective Material The handleability of the surface protective material was evaluated as to whether or not the epoxy resin composition was transferred when it was brought into contact with rubber gloves (made of nitrile rubber). If the epoxy resin composition was transferred only from the resin side of the surface protective material and not from the other side (the fiber side, except for Comparative Example 1), it was rated as "good." Furthermore, if the epoxy resin composition was not transferred from the surface protective material to the rubber gloves from either side during handling, it was rated as "very good." If the resin was transferred to both sides of the surface protective material, it was rated as "poor."

[0122] (6) Measurement of gaps in nonwoven fabric substrates The nonwoven fabric substrate was cut into a size of 10 cm x 10 cm square to prepare a sample, and the nonwoven fabric substrate portion and the gap portion were easily distinguished (the nonwoven fabric substrate was attached to drawing paper of a different color from the nonwoven fabric substrate). An observation image was obtained at 100x magnification using an optical microscope (VHX-5000 (manufactured by Keyence Corporation)). The obtained observation image was binarized using ImageJ / Fiji to determine the gap portion and the nonwoven fabric substrate portion, and the gap (%) was calculated by determining the ratio of the gap portion area on the observation image to the total area of ​​the observation image. The gap was determined for each of five nonwoven fabric substrates cut into a 10 cm x 10 cm square by selecting an arbitrary position, and the average value was calculated. (7) Measurement of orientation distribution f of reinforcing fibers constituting nonwoven fabric substrate The nonwoven fabric substrate was cut into a size of 10 cm x 10 cm square to prepare a sample, and an arbitrary location of the sample was observed in transmitted light mode using an optical microscope (VHX-5000 (manufactured by Keyence Corporation)), and an observation image was obtained at a magnification of 500 times. In the obtained observation image, the number of reinforcing fibers (n in the above formula 1) was counted, a baseline was arbitrarily drawn, and a straight line was manually drawn one by one throughout the range of the observation image in the tangential direction of the center of each reinforcing fiber in the observation image. Here, the center of the reinforcing fiber in the observation image is the position of the reinforcing fiber that is equidistant from both ends of the reinforcing fiber within the range of the observation image. The angle between the baseline and the straight line was determined and used as the angle of the reinforcing fiber with respect to the baseline. Here, when the reinforcing fibers cross and overlap front and back in the observation image, the rear reinforcing fibers were measured assuming that they were continuous behind the front reinforcing fibers. The orientation distribution f of the nonwoven fabric substrate was calculated from the above formula 1. The orientation distribution f was determined for each of five pieces of nonwoven fabric substrate cut into a square of 10 cm x 10 cm selected at any position, and the average value of the obtained orientation distribution f was used.

[0123] Examples 1 to 13 In Examples 1 to 13, surface protection materials were produced using epoxy resin compositions in which the blending amounts of the components [A] to [E] and the types of blended raw materials were changed, and using the two types of nonwoven fabric substrates described above, under the impregnation conditions shown in the table for the two types of evacuation times shown in the table.

[0124] In Examples 1 and 2, surface protection materials were prepared using the same epoxy resin composition and nonwoven fabric substrate, but with different impregnation conditions. Although some resin transfer to the worker's gloves was observed with both surface protection materials, handling was good. The maximum pinhole diameter was less than 400 μm in all cases, and a comparison based on the impregnation conditions showed that Example 2, which reduced the degree of impregnation by shortening the vacuuming time, reduced the occurrence of pinholes after storage at room temperature.

[0125] In Example 3, a surface protective material was produced by impregnating a different nonwoven fabric substrate from that of Example 1 using the same epoxy resin composition as in Example 1 under the same conditions as in Example 1. As a result, the surface protective material of Example 3 showed less pinholes than the surface protective material of Example 2 after storage at room temperature.

[0126] In Examples 4 to 13, the blending amounts and raw material types of components [A] to [E] were changed from those in Example 3, and surface protective materials were produced using the same nonwoven fabric substrate as in Example 3 under the same impregnation conditions as in Example 3. It was shown that the higher the Casson yield value of the epoxy resin composition, the more likely it is that the maximum diameter of pinholes observed in the surface protective material after storage at room temperature will be suppressed. The Casson yield value improved significantly as the blending amount of component [B] increased, followed by an improvement as the blending amount of component [D] increased.

[0127] In Example 8, the type of component [B] was changed based on Example 9. Although the blending amounts were the same, the epoxy resin composition of Example 8 had a lower Casson yield value and a larger maximum pinhole diameter than the epoxy resin composition of Example 9.

[0128] In Example 5, the type of component [D] was changed based on Example 9. Although the blending amounts were the same, the epoxy resin composition of Example 5 had a lower Casson yield value and a larger maximum diameter of pinholes observed in the surface protective material after storage at room temperature, compared to the epoxy resin composition of Example 9.

[0129] In Examples 6 and 7, the same component [D] was used as in Example 5, but the blending amount was increased. In these cases, an improvement in the Casson yield value was observed, and no pinholes were observed after the surface protection material was stored at room temperature.

[0130] The handleability of the surface protective materials in Examples 6, 7, and 9 to 13 was extremely good, with no resin transfer to the gloves of the workers during handling. <Examples 9, 14, and 15> In Examples 14 and 15, the impregnation conditions were changed compared to Example 9. In Example 14, the vacuuming time was shortened to reduce the degree of impregnation compared to Example 9, and no pinholes were generated after the surface protective material was stored at room temperature. On the other hand, in Example 15, the vacuuming time was lengthened compared to Example 9 to increase the degree of impregnation, and the maximum pinhole diameter was slightly increased compared to Example 9. <Examples 1, 9, Comparative Examples 1 to 5> In Comparative Example 1, a similar evaluation was performed using the epoxy resin composition prepared in Example 1 and a resin film that did not contain a nonwoven fabric substrate. The resin film alone lost its shape and was difficult to handle.

[0131] In Comparative Example 2, a surface protective material was produced using an epoxy resin composition obtained by omitting component [B] from the epoxy resin composition of Example 1. As a result, although the surface protective material was able to be handled, the maximum diameter of the pinholes was large, and the appearance of the surface protective material was impaired.

[0132] In Comparative Example 3, a surface protective material was produced using the same resin composition and nonwoven fabric substrate as in Example 9, but with a lower resin content than in Example 9. As a result, the maximum diameter of pinholes was large, and the appearance of the surface protective material was impaired.

[0133] In the above-described Examples and Comparative Examples 1 to 3, the quality of the resin films was good, but in Comparative Examples 4 and 5, a resin with a Casson yield value of more than 1000 Pa was used, and film formation was attempted using a knife coater. However, a large number of streaky areas where the epoxy resin was not applied occurred, and it was not possible to produce a resin film of good quality. <Examples 9 and 16 to 30> In Examples 16 to 18, the type of component [B] of the epoxy resin composition was changed based on Example 9. Although the blending amounts were the same, the epoxy resin compositions of Examples 16 to 18 had higher Casson yield values ​​and smaller maximum pinhole diameters than the epoxy resin composition of Example 9.

[0134] In Examples 19 to 21, the resin content of the surface protective material was changed based on Example 9. In Examples 19 and 20, the maximum diameter of pinholes increased as the resin content was reduced from that of Example 9. In Example 21, the resin content was higher than in Example 9, and no pinholes were observed.

[0135] In Examples 22 to 24, the type of nonwoven fabric substrate was changed based on Example 9. From the perspective of the gaps in the nonwoven fabric substrate, in Example 22, the gaps in the nonwoven fabric substrate were larger than in Example 9, and the maximum diameter of the pinholes was larger. In Examples 23 to 24, the smaller the gaps were compared to Example 9, the smaller the maximum diameter of the pinholes was. Next, from the perspective of the orientation distribution f of the reinforcing fibers constituting the nonwoven fabric substrate, in Example 22, the value of f was lower than in Example 9, and the maximum diameter of the pinholes was larger. In Examples 23 to 24, the value of f was higher than in Example 9, and the maximum diameter of the pinholes was larger.

[0136] In Examples 25 to 27, the types of component [A] and component [C] were changed based on Example 9. In Example 25, the type of component [A] was changed from Celloxide 2021P to EPALLOY 5000 compared to Example 9. As a result, the maximum diameter of pinholes was smaller than that of Example 9. In Example 26, the type of component [C] was changed from San-Aid SI-100 to jER Cure DICY7 compared to Example 9, and a curing accelerator was added. As a result, the maximum diameter of pinholes was larger than that of Example 9. In Example 27, the type of component [A] was changed from Celloxide 2021P to EPALLOY 5000, and the type of component [C] was changed from San-Aid SI-100 to jER Cure DICY7 compared to Example 9, and a curing accelerator was added. As a result, the maximum diameter of pinholes was smaller than that of Example 9.

[0137] In Examples 28 and 29, the evacuation time under the impregnation conditions was shortened compared to Example 9. As a result, the WPU value increased and no pinholes were observed.

[0138] A nonwoven fabric substrate made of PET fiber was used in Example 30. The maximum diameter of pinholes was larger than in Examples 9 and 22 to 24, which used a nonwoven fabric substrate made of glass fiber but had the same epoxy resin composition, resin content, and impregnation conditions.

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[0143] REFERENCE SIGNS LIST 1: Nonwoven fabric substrate 2: Epoxy resin composition 3: Surface protective material 4: Fiber surface 5: Resin surface

Claims

1. A surface protection material comprising a nonwoven fabric substrate at least partially impregnated with an epoxy resin composition containing components [A] to [C], the content of the epoxy resin composition being in the range of 75 to 98 mass %. [A] non-aromatic epoxy resin [B] thixotropic agent [C] curing agent 2. The surface protective material according to claim 1, wherein the nonwoven fabric substrate contains glass fibers.

3. The surface protective material according to claim 1 or 2, wherein the nonwoven fabric substrate contains fibers having a fiber diameter of 3 to 20 μm.

4. The surface protective material according to claim 1 or 2, wherein the nonwoven fabric substrate contains short fibers having a fiber length of 2 to 30 mm.

5. The surface protective material according to claim 1 or 2, having a WPU value of 0.5 to 10%.

6. The surface protective material according to claim 1 or 2, wherein the degree of exposure of the nonwoven fabric substrate is different on both surfaces of the surface protective material.

7. The surface protective material according to claim 1 or 2, wherein the orientation distribution f of the reinforcing fibers in the nonwoven fabric substrate is 0.300 to 0.

637.

8. The surface protective material according to claim 1 or 2, wherein the nonwoven fabric substrate has a void ratio of 3 to 35%.

9. The surface protective material according to claim 1 or 2, wherein the epoxy resin composition has a Casson yield value at 74°C in the range of 70 to 1,000 Pa.

10. Component [B] has a specific surface area of ​​60 to 300 m ２ The surface protective material according to claim 1 or 2, wherein the surface protective material has a viscosity of 1 / g.

11. The surface protective material according to claim 1 or 2, wherein component [B] is contained in an amount of 3 to 14 parts by mass when the total amount of the epoxy resin is taken as 100 parts by mass.

12. The surface protective material according to claim 1 or 2, further comprising a component [D], wherein the amount of component [D] is 20 to 70 parts by mass when the total amount of the epoxy resin is 100 parts by mass. [D] Non-aromatic thermoplastic resin 13. A molded article obtained by curing the surface protective material according to claim 1 or 2 or a laminate in which a plurality of said surface protective materials are laminated.

14. A surface-protected fiber-reinforced composite material obtained by affixing a surface protective material according to claim 1 or 2 to the outermost surface of one or both sides of a fiber-reinforced composite material precursor, which is a single layer of prepreg or a laminate of multiple layers of prepreg, and then curing the surface-protected fiber-reinforced composite material.

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