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

Abstract

The present invention addresses the problem of providing a surface protective material which has excellent light resistance, can be disposed on a single layer of a composite material precursor or the outermost surface of a laminate to protect the surface of a base material of a fiber-reinforced composite material and prevent deterioration due to light, can suppress mixing of a base resin having poor light resistance and an epoxy resin composition having light resistance during thermal curing, and can be used on the surface of a fiber-reinforced composite material precursor to impart good appearance and robust resistance.　The surface protective material is obtained by impregnating a fiber base material with an epoxy resin composition containing components [A], [D], and [C], wherein the surface area of the fiber base material per unit area is 2.0-30 (m2 / m2). [A] non-aromatic epoxy resin, [D] non-aromatic thermoplastic resin, [C] 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 for producing a surface protective material by applying an epoxy resin composition containing a non-aromatic epoxy resin using a spray or a bar coater and then curing the applied composition. It also describes that by pre-curing the precursor to be protected, it is possible to reduce the amount of the resin contained in the surface protective material and the resin contained in the precursor of the fiber-reinforced composite material to be protected that mixes with each other during heating and / or pressure curing.

[0005] Furthermore, Patent Document 3 describes a fiber-reinforced composite material, and gives 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 a nonwoven fabric is impregnated with the pre-cured resin to form a prepreg. The document describes that by pre-curing the prepreg to reduce the resin flow, when different materials such as precursors of other fiber-reinforced composite materials are combined, the amounts of the thermosetting resins that are mixed together during the molding process can be reduced.

[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 fiber 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 inventions described in Patent Documents 2 and 3, a process of semi-curing the material is necessary to solve the above-mentioned problem of mixing the resins, which makes the manufacturing process complicated.

[0009] The present invention was achieved by focusing on the phenomenon of resin mixing described above in relation to the fibrous base material contained in the surface protective material.

[0010] That is, the present invention has discovered that the use of a fiber substrate contained in a surface protective material can suppress mixing of the resin contained in the surface protective material and the resin contained in the fiber-reinforced composite material precursor to be protected during curing. 1. A surface protective material obtained by impregnating a fiber substrate with an epoxy resin composition containing components [A], [D], and [C], wherein the surface area of ​​the fiber substrate per unit area is 2.0 to 30 (m ２ / m ２ ), and the value obtained by multiplying the surface area of ​​the fiber substrate per unit area by the thickness of the surface protection material is 150 to 2000 (× 10-6 (m ２ ・m) / m ２ [A] a non-aromatic epoxy resin; [D] a non-aromatic thermoplastic resin; and [C] a curing agent. 2. The flow index of the epoxy resin composition is 0.05 to 1.5 (Pa s). －１3. The surface protective material according to any one of 1 to 3 above, wherein the voids of the fiber substrate are 3 to 35%. 5. The surface protective material according to any one of 1 to 4 above, wherein the fiber substrate contains glass fiber. 6. The surface protective material according to any one of 1 to 5 above, wherein the fiber substrate has the form of a nonwoven fabric substrate or a woven fabric. 7. The surface protective material according to 6 above, wherein the fiber substrate has the form of a nonwoven fabric substrate and the voids of the fiber substrate are 3 to 35%. 8. The surface protective material according to 6 above, wherein the fiber substrate has the form of a woven fabric and the voids of the fiber substrate are 3 to 25%. 9. The surface protective material according to 6 above, wherein the fiber substrate has the form of a nonwoven fabric substrate and the surface area of ​​the fiber substrate is 2.0 to 7.0 (m ２ / m ２ 10. The surface protective material according to 6 or 7 above, wherein the fiber substrate has a woven fabric form and a surface area of ​​the fiber substrate is 3.0 to 30 (m ２ / m ２ 11. The surface protective material according to 6 or 8 above, wherein the fiber substrate has the form of a woven fabric, and the number of fibers constituting the yarn bundles in the warp direction and the fill direction is 20 to 80. 12. A surface-molded body obtained by curing the surface protective material according to any one of 1 to 11 above, or a laminate comprising a plurality of said surface protective materials. 13. 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 11 attached to the outermost surface on one or both sides of said fiber-reinforced composite material precursor.

[0011] According to the present invention, it is possible to prevent the resin contained in the surface protective material from mixing with the resin contained in the fiber-reinforced composite material precursor to be protected during curing.

[0012] 1A and 1B are cross-sectional views in the thickness direction of the surface protective material of the present invention, showing a large difference in the degree of exposure of the fiber substrate on both surfaces, and a cross-sectional view in the thickness direction of the surface protective material of the present invention, showing no difference in the degree of exposure of the fiber substrate on both surfaces.

[0013] 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.

[0014] 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.

[0015] "Overview" The surface protective material of the present invention is a material in which a fiber substrate is at least partially impregnated with an epoxy resin composition. Here, "at least partially impregnated" means that the fiber substrate in the surface protective material may have some regions in the thickness direction that are 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 in which a single layer or multiple layers of so-called prepregs are laminated, a material in which reinforcing fibers are impregnated with a thermosetting resin. 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 the composite material precursor.

[0016] 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.

[0017] By including a fibrous base material, the surface protective material of the present invention becomes easy to handle because the fibrous base material serves as a support for the epoxy resin composition.

[0018] On the other hand, there is a problem in that it is necessary to suppress the phenomenon in which the epoxy resin composition contained in the surface protective material and the resin contained in the composite material precursor to be protected mix together when the viscosity is reduced at high temperatures during curing (hereinafter referred to as the "mixing phenomenon"). If the mixing phenomenon occurs frequently, the resin of the composite material precursor, which is not necessarily light-resistant, is exposed to a large extent on the outermost surface of the surface-protected fiber-reinforced composite material, and sufficient light resistance cannot be obtained.

[0019] In response to the above-mentioned problems, the present inventors have considered the possibility of suppressing the intermixing phenomenon by using an epoxy resin composition that is less likely to flow during the curing process. Furthermore, they have considered that by using a fiber base material with a large surface area as a surface protection material, the fiber base material will prevent the resin contained in the composite material precursor from penetrating into the surface protection material during the curing process, thereby suppressing the intermixing phenomenon.

[0020] Therefore, the present inventors have developed a method for manufacturing a surface protective material having a surface area (unit: m) of a fiber substrate per unit area of ​​the surface protective material, in which the epoxy resin composition contains a non-aromatic thermoplastic resin and the surface area (unit: m) of the fiber substrate per unit area of ​​the surface protective material is small. ２ / m ２ ) from 2.0 to 30 (m ２ / m ２ ) can further suppress the mixing phenomenon and provide a surface protective material with excellent handleability. Here, the surface area of ​​the fiber substrate per unit area of ​​the surface protective material represents the total surface area of ​​the fiber substrate relative to the unit area that covers the object to be protected as a surface protective material. Hereinafter, "surface area of ​​the fiber substrate per unit area of ​​the surface protective material" may be abbreviated as "surface area of ​​the fiber substrate." Furthermore, "non-aromatic thermoplastic resin" is a thermoplastic resin that does not have a ring structure that satisfies Hückel's rule.

[0021] The surface area (m ２ / m ２ ) is 3.0 to 30 (m ２ / m ２ ), and 5.0 to 30 (m ２ / m２ ), and more preferably 10 to 30 (m ２ / m ２ It is more preferable that the surface area of ​​the fiber substrate is 2.0 (m ２ / m ２ ) or more, the fiber substrate can prevent the resin of the composite material precursor from penetrating during the curing process, and the mixing phenomenon can be further suppressed. ２ / m ２ ) or less, the surface protective material will have good shapability.

[0022] In the present invention, the surface area (m ２ / m ２ ) is calculated by assuming that each fiber is cylindrical, ignoring the area of ​​its base, and calculating only the side area (fiber diameter multiplied by pi and fiber length) as the surface area of ​​each fiber (m ２ Specifically, it is defined as the fiber substrate basis weight of the surface protective material multiplied by 4, divided by the product of the fiber substrate density and fiber diameter, and calculated using the following formula.

[0023] (weight per unit area of ​​fiber substrate) × 4 / (density of fiber substrate × fiber diameter of fiber substrate) Here, in the present invention, the density of the fiber substrate (unit: g / cm ３ ) is determined in accordance with JIS Z 8807: 2012. Note that, in order to determine the fiber base material basis weight from the surface protective material, the density may be determined using a fiber base material extracted by a method using a solvent as described below.

[0024] Fiber substrate weight (unit: g / m ２ ) and resin basis weight (unit: g / m ２ The surface protection material is first cut into a 10 cm x 10 cm square sample, its mass is measured, and the area (100 cm 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 at 100° C. for 15 minutes or more), and only the fiber substrate is extracted. The mass of the extracted fiber substrate is measured, and the area (100 cm ２ When the surface protective material consists only of an epoxy resin composition and a fiber substrate, the resin basis weight is calculated by subtracting the fiber substrate basis weight from the surface protective material basis weight.

[0025] Any of the above-mentioned basis weights was measured by measuring the above-mentioned 100 cm from five points arbitrarily selected from the surface protection material. ２ If it is necessary to measure the fiber substrate density, similarly measure 100 cm ２ Five samples are taken, and each is measured once, and the average value of the five measurements is used. ２ If five samples cannot be taken, the value obtained from the available samples may be used.

[0026] The mixing phenomenon was confirmed by measuring the surface protection material side of the surface-protected fiber-reinforced composite material by an ATR method, and detecting a peak value specific to the surface protection material (for example, 1715 cm indicating an ester group). －１ The peak value specific to the compound contained in the fiber-reinforced composite material precursor (for example, 1592 cm indicating a benzene ring) is normalized. －１ The amount of resin in the composite material precursor exposed to the surface-protected fiber composite material is measured using, for example, an FT / IR-4000 (manufactured by JASCO Corporation). Details of other measurement methods are as described in (2) Amount of resin in the composite material precursor exposed to the surface-protected fiber composite material in Examples, but other methods may be used as long as they can obtain the same results.

[0027] "Surface protection material" A surface of a surface protection material with a large degree of exposure of the fiber substrate, such as the upper surface in Figure 1, is less susceptible to adhesion (contamination) of the epoxy resin composition to gloves, etc., during the process of attaching the surface protection material to a composite material precursor, and provides good handleability, compared to a surface with a small (or no) exposure of the fiber substrate, such as the upper surface in Figure 2.

[0028] To produce a surface protective material with a highly exposed fiber substrate, such as the upper surface in Figure 1 , it is recommended to impregnate the fiber substrate with the epoxy resin composition only from one side of the fiber substrate (single-sided impregnation). This impregnation method facilitates exposing the fiber substrate on one side of the surface protective material. Hereinafter, the side of the surface protective material where the fiber substrate is present inside the resin and not exposed will be referred to as the resin side (reference numeral 5 in Figures 1 and 2 ), and the side where the fiber substrate is exposed will be referred to as the fiber side (reference numeral 4 in Figure 1 ). Single-sided impregnation facilitates forming a resin side on one side and a fiber side on the opposite side. The exposure of the fiber 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 fiber 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 fiber base material on both sides decreases, approaching the state shown in FIG.

[0029] In the surface protective material of the present invention, the surface area of ​​the fiber substrate is multiplied by the thickness of the surface protective material (unit: m) (unit: × 10 －６ (m ２ ・m) / m ２ ) is 150 to 2000 (x 10 －６ (m ２ ・m) / m ２ ), and 200 to 1500 (×10 －６ (m ２ ・m) / m ２ ), more preferably 300 to 1500 (×10 －６ (m ２ ・m) / (m ２ )) is more preferably 400 to 1500 (×10 －６ (m ２ ・m) / (m ２It is more preferable that the surface area of ​​the fiber substrate multiplied by the thickness of the surface protection material is 200 (×10 －６ (m ２ ・m) / m ２ ) or more is preferable because the mixing phenomenon can be further suppressed in the surface protective material, and －６ (m ２ ・m) / m ２ ) or less, the surface protective material has excellent shapability, which is preferable.

[0030] When the surface protective material is composed only of an epoxy resin composition and a fiber base material, the thickness (m) of the surface protective material is calculated using the following formula, ignoring voids within the surface protective material.

[0031] Resin basis weight / resin density+fiber substrate basis weight / fiber substrate density Here, the resin density refers to the density of the cured product of the epoxy resin composition.

[0032] Resin density (unit: g / cm ３ ) is determined in accordance with JIS Z 8807:2012. Resin density is measured using a cured product of the epoxy resin composition (hereinafter referred to as the "cured epoxy resin product") cut to a width of 1 cm and a length of 5 cm. The cured epoxy resin product is obtained by casting the epoxy resin composition into a 2 mm thick mold, heating it to 180°C in an oven at a rate of 1.7°C / min, holding it at 180°C for 2 hours, and then demolding it. In measuring the resin density, the surface protective material may be sandwiched between release papers and heated and compressed with an iron to transfer only the epoxy resin composition to the release paper, which is then recovered and used to prepare a cured epoxy resin product. The fiber substrate basis weight and fiber substrate density are determined using the methods described above. In both the fiber substrate and the resin composition, density refers to true density, which is the density calculated from the actual volume of each material itself, excluding spaces between fibers and air bubbles. "Fiber Substrate": The fiber substrate used in the present invention may take the form of a woven fabric, a nonwoven fabric, a mesh, or the like. Among these, surface protective materials using a woven or nonwoven fabric substrate as the fiber substrate are preferred because they are easy to handle and are excellent in suppressing the mixing phenomenon.

[0033] In the present invention, the woven fabric refers to a substrate made by interlacing fill yarns and warp yarns, or a substrate made by interlacing multiaxial yarns.

[0034] When a woven fabric is used as the fiber substrate, the surface protective material is preferably highly resistant to tearing during handling.

[0035] When a woven fabric is used as the fiber substrate, it is preferable that each of the warp (Fill) and weft (Warp) yarn bundles is composed of 20 to 80 reinforcing fibers, and the number of reinforcing fibers constituting each yarn bundle is more preferably 20 to 70, and even more preferably 30 to 70. When the number of reinforcing fibers constituting the reinforcing fibers used in the woven fabric is 20 or more, the gaps become larger than a certain amount, which is preferable because the shaping ability of the surface protective material is superior. When the number of such fibers is 80 or less, the gaps do not become excessively large, and the mixing phenomenon can be further suppressed, which is preferable.

[0036] When a woven fabric is used as the form of the fiber substrate, the surface area of ​​the fiber substrate is 3.0 to 30 (m ２ / m ２ ), and 4.5 to 30 (m ２ / m ２ ), and more preferably 10 to 30 (m ２ / m ２ ), and more preferably 10 to 20 (m ２ / m ２ ), and more preferably 15 to 20 (m ２ / m ２ When it is in the form of a woven fabric, the surface area per unit area is preferably 3.0 (m ２ / m ２ ) or more, the mixing phenomenon can be further suppressed. ２ / m ２ ) or less, the surface protective material will have good shapability.

[0037] Furthermore, when a nonwoven fabric substrate is used as the fiber substrate, the surface protective material is highly resistant to distortion during handling, which is preferable.

[0038] In the present invention, the nonwoven fabric substrate refers to a reinforcing fiber sheet, web, or pad, excluding woven fabric, taffeta, and felted felt, in which the reinforcing fibers are oriented in one direction or randomly and the reinforcing fibers are bonded together by any one or a combination of entanglement, fusion, and adhesion. The method for producing the nonwoven fabric substrate is not particularly limited, but the web formation method may be a dry method, a wet method, or a spunbonding method, and the bonding method between the reinforcing fibers may be needle punching, chemical bonding, thermal bonding, spunlace, or the like.

[0039] When a nonwoven fabric substrate is used as the fiber substrate, the reinforcing fibers constituting the nonwoven fabric substrate may be in the form of either continuous or short fibers. However, short fibers are preferred because the reinforcing fibers in the surface protective material overlap more, increasing bulk, resulting in high rigidity and easy handling of the surface protective material. When the reinforcing fibers constituting the nonwoven fabric substrate are short fibers, the fiber length is preferably 2 to 30 mm, more preferably 2 to 15 mm, and even more preferably 4 to 13 mm. A fiber length of 2 mm or more increases the contact area between the reinforcing fibers of the nonwoven fabric substrate and the resin of the composite material precursor, making it possible to further suppress the mixing phenomenon. A fiber length of 30 mm or less increases the overlapping portions of the reinforcing fibers, reducing the breathability of the nonwoven fabric substrate and enhancing the ability to stop the flow of the resin of the composite material precursor during the curing process.

[0040] When a nonwoven fabric substrate is used as the fiber substrate, the surface area of ​​the fiber substrate is 2.0 to 7.0 (m ２ / m ２ ), and 3.0 to 7.0 (m ２ / m ２ ), and more preferably 3.0 to 6.0 (m ２ / m ２ ), and more preferably 5.0 to 6.0 (m ２ / m ２ When it is in the form of a woven fabric, the surface area per unit area is preferably 2.0 (m ２ / m ２ ) or more is preferable because the mixing phenomenon can be further suppressed. ２ / m ２) or less, the surface protective material has excellent shapeability, which is preferable.

[0041] Examples of reinforcing fibers constituting the fiber 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.

[0042] The tensile modulus of the reinforcing fibers constituting the fiber 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, and better handleability can be achieved. When the tensile modulus is 350 GPa or less, the reinforcing fiber does not have a high modulus, and therefore the shapeability of the surface protective material is better, which is preferable. Specifically, glass fiber is preferably used as a reinforcing fiber having a tensile modulus in this range.

[0043] The tensile modulus is an average value obtained by measuring 20 reinforcing fibers according to JIS R 7606:2000 (calculation method: Method A).

[0044] The tensile modulus may be measured by extracting reinforcing fibers from the fiber substrate extracted by the method described above for measuring the basis weight of the substrate in the surface protective material. When the fiber length of the reinforcing fibers constituting the fiber substrate is shorter than 25 mm, the sample length may be changed accordingly.

[0045] The fiber diameter of the fiber substrate is preferably 3 to 15 μm, more preferably 3 to 10 μm, even more preferably 3 to 8 μm, and even more preferably 5 to 8 μm. When the fiber diameter is 3 μm or more, the surface protective material has firmness and good handleability, and when the fiber diameter of the reinforcing fiber is 15 μm or less, the surface area of ​​the fiber substrate is large, which is preferable because it can further suppress the mixing phenomenon. Compared to when the fiber substrate is in the form of a nonwoven fabric, when it is a woven fabric, there is a concern that it may have poor shapeability. Therefore, in order to maintain shapeability, it is preferable to use reinforcing fibers with a relatively small diameter, specifically 3 to 5.5 μm, and more preferably 3 to 5 μm.

[0046] When it is necessary to measure the fiber length and fiber diameter (diameter), the fiber substrate is observed under an optical microscope, 20 reinforcing fibers are arbitrarily selected from the observation image, their fiber lengths and fiber diameters are measured, and the averages are calculated. Note that the fiber substrate may be extracted by the method using the above solvent.

[0047] When a woven fabric is used as the fiber substrate, the gap is preferably 3 to 25%, more preferably 3 to 20%, even more preferably 3 to 15%, and even more preferably 3 to 10%. When the gap of the woven fabric is 3% or more, the drapeability of the surface protective material is improved and handling is better. When the gap of the woven fabric is 25% or less, the gaps in the fiber substrate are reduced, thereby improving the function of stopping the flow of the resin in the composite material precursor during the curing process. When a nonwoven fabric substrate is used as the fiber substrate, the gap 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 woven fabric is 3% or more, the drapeability of the surface protective material is improved and handling is better. When the gap of the nonwoven fabric substrate is 35% or less, the gaps in the fiber substrate are reduced, thereby improving the function of stopping the flow of the resin in the composite material precursor during the curing process.

[0048] The voids in the fiber 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 below. In the present invention, the epoxy resin composition refers to a mixture containing an epoxy resin, a curing agent, and other components.

[0049] 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.

[0050] The flow index, which is an index of the curing of an epoxy resin composition and the flow during curing, can also be an index for understanding the mixing phenomenon. Here, the flow index is determined by dynamic viscoelasticity measurement (an apparatus such as an ARES-G2 (manufactured by TA Instruments) can be used). Details of the measurement method are described below in the examples, but different methods may be used as long as the same results can be obtained. The flow index can be measured for an epoxy resin composition obtained by a method in which a surface protective material is sandwiched between release papers and heated and compressed with an iron to transfer only the epoxy resin composition to the release paper, which is then recovered and extracted.

[0051] The flow index of the epoxy resin composition at 20 to 100°C is preferably 0.05 to 1.5 (1 / Pa s), more preferably 0.05 to 0.5 (1 / Pa s), even more preferably 0.05 to 0.3 (1 / Pa s), and particularly preferably 0.05 to 0.2. A flow index of 0.05 (1 / Pa s) or more is preferred because it exhibits more appropriate resin flow during curing, making it easier to fill defects on the surface of the surface-protected fiber-reinforced composite material that have not been filled with the epoxy resin composition, thereby achieving a good appearance. A flow index of 1.5 (1 / Pa s) or less is preferred because it reduces resin flow and makes it possible to further suppress the mixing phenomenon. "Component [A]" The epoxy resin composition used in the present invention contains a non-aromatic epoxy resin (component [A]).

[0052] When the epoxy resin composition contains a non-aromatic epoxy resin, light resistance is imparted to the surface protective material after curing.

[0053] 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 flow index is lowered, and the mixing phenomenon can be further suppressed. When the viscosity is 1,000,000 Pa·s or lower, resin film formation is facilitated. The viscosity of the non-aromatic epoxy resin is measured at 25°C in accordance with JIS K 5600-2-3:2014.

[0054] 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, the surface protective material can be imparted with better light resistance, and a surface-protected fiber-reinforced composite material having better appearance and light resistance can be obtained.

[0055] Non-aromatic epoxy resins include aliphatic epoxy resins and alicyclic epoxy resins.

[0056] 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.

[0057] Examples of such epoxidized cycloalkanes are represented by the following chemical structures:

[0058]

[0059] 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.).

[0060] Examples of compounds containing the 1,2-epoxycycloalkane structure are represented by the following chemical structures:

[0061]

[0062]

[0063] 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 preferably contains a thixotropic agent (component [B]).

[0064] When the epoxy resin composition contains a thixotropic agent, the flow index decreases, and the mixing phenomenon is further suppressed.

[0065] 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 R 1665:2005. The higher the thixotropy, the lower the flow index.

[0066] In order 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 to improve the thixotropy of the epoxy resin composition, 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 between the thixotropic agents increases, the thixotropy of the epoxy resin composition is improved, the flow index is lowered, and the mixing phenomenon can be further suppressed. ２ When the specific surface area of ​​the thixotropic agent is 1 / g or less, there are few coarse aggregates of the thixotropic agent in the epoxy resin composition, and the thixotropic agent can be well dispersed 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 is measured according to JIS Z 8830:2013 (BET method).

[0067] The thixotropic agent is preferably contained in an amount of 3 to 14 parts by mass, 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 dispersion of the thixotropic agent in the epoxy resin composition is improved, and the effect per unit amount of the thixotropic agent can be further increased.

[0068] Examples of the thixotropic agent include silica containing silicon dioxide, synthetic hectorite, clay minerals, bentonite, and a mixture of organically modified bentonite.

[0069] 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 CABOT Corporation). Examples include "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, and Micromica MK (manufactured by Katakura Co-op Agri Co., Ltd.).

[0070] 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.

[0071] 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.

[0072] 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).

[0073] 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). Among these, sulfonium salts can impart low-temperature curing properties to the epoxy resin composition, lower the flow index, and further suppress the mixing phenomenon.

[0074] 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.

[0075] 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].

[0076] 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.

[0077] When an aliphatic epoxy resin or an alicyclic epoxy resin corresponding to an epoxidized cycloalkane is used as component [A], it is preferable to use an amine-based curing agent or an anionic curing agent as component [C], since this can impart low-temperature curing properties to the epoxy resin composition and further suppress the above-mentioned mixing phenomenon. "Component [D]" The epoxy resin composition used in the present invention contains a non-aromatic thermoplastic resin (component [D]).

[0078] By including such a non-aromatic thermoplastic resin, the viscosity of the epoxy resin composition is increased, and therefore the mixing phenomenon can be suppressed.

[0079] 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 the total epoxy resin 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 the mixing phenomenon can be further suppressed. Furthermore, when the amount is 70 parts by mass or less, the ease of forming a resin film is excellent, which is preferable.

[0080] 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 viscosity of the epoxy resin composition increases and the flow index decreases, thereby further suppressing the mixing phenomenon. Here, the number average molecular weight refers to the number average molecular weight calculated in terms of polystyrene by gel permeation chromatography.

[0081] 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.

[0082] 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.).

[0083] 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.

[0084] 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.

[0085] 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]).

[0086] 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 further suppress the penetration of UV into the fiber-reinforced composite material, resulting in 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.

[0087] 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.

[0088] "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.

[0089] "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 fibrous 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 fibrous substrate, or by disposing the resin film on only one side of the fibrous 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.

[0090] The surface protective material can also be produced by directly applying the epoxy resin composition to a substrate and impregnating it.

[0091] 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.

[0092] "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.

[0093] 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.

[0094] 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.

[0095] "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.

[0096] 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.

[0097] <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, average particle size 0.5 μm) (6) Fiber base material Grabestos EVP-017 (glass fiber nonwoven fabric, polyvinyl alcohol (PVA) binder used) (manufactured by Olivest Co., Ltd., fiber base material basis weight 17 g / m ２ , fiber diameter 6 μm, fiber length 6 mm, fiber substrate density 2.6 g / cm ３ Grabestos EVP-020 (glass fiber nonwoven fabric, polyvinyl alcohol (PVA) binder used) (Olivest Co., Ltd., fiber substrate basis weight 20 g / m ２ , fiber diameter 6 μm, fiber length 6 mm, fiber substrate density 2.6 g / cm ３ Grabestos EVP-023 (glass fiber nonwoven fabric, polyvinyl alcohol (PVA) binder used) (Olivest Co., Ltd., fiber substrate basis weight 23 g / m ２ , fiber diameter 6 μm, fiber length 6 mm, fiber substrate density 2.6 g / cm ３ ) Optiveil 20103A (glass fiber nonwoven fabric, PVA binder used) (tfp, fiber substrate basis weight 10 g / m ２ , fiber diameter 11 μm, fiber length 15 mm, fiber substrate density 2.6 g / cm ３ ) Optiveil 20103A (glass fiber nonwoven fabric, PVA binder used) (tfp, fiber base material basis weight 17 g / m ２ , fiber diameter 11 μm, fiber length 15 mm, fiber substrate density 2.6 g / cm ３) Optiveil 20254A (PET fiber nonwoven fabric, polyester binder used) (tfp, fiber substrate basis weight 12 g / m 2, fiber diameter 6 μm, fiber length 5 mm, fiber substrate density 1.4 g / cm ３ ) E01Z 4W 106KH (glass fiber fabric, binder-free) (manufactured by Unitika Ltd., fiber base material basis weight: 12.5 g / m ２ , fiber diameter 4 μm, fiber substrate density 2.6 g / cm ３ ) Style 108 glass fabric (glass fiber fabric, epoxy binder used) (manufactured by JPS, fiber base material basis weight 48 g / m ２ , fiber diameter 5 μm, fiber substrate density 2.6 g / cm ３ ) Style 15695 Glass Fabric (Glass Fiber Fabric, Epoxy Binder Used) (Manufactured by JPS, Fiber Base Material Weight 48 g / m ２ , fiber diameter 5 μm, fiber substrate density 2.6 g / cm ３ ) Style 1280 glass fabric (glass fiber fabric, epoxy binder used) (manufactured by JPS, fiber base material weight 53 g / m ２ , fiber diameter 5 μm, fiber substrate density 2.6 g / cm ３ (7) Prepreg (surface protection target) - T800S / 3900-2B (continuous fiber) prepreg (manufactured by Toray Industries, Inc.).

[0098] (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.

[0099] (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.

[0100] 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.

[0101] (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.

[0102] The resin film having good quality shown in the table means that it does not fall into either of the above a and b.

[0103] (3) Preparation of surface protective material One resin film prepared in (2) was placed on one side of a fiber substrate, and then both sides of the film were sandwiched between release papers and vacuumed (carried out at 76 cmHg) to impregnate the fiber substrate with the epoxy resin composition, thereby obtaining 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 fiber substrate to form a resin surface, and part of the epoxy resin composition in the resin layer had impregnated the fiber substrate.

[0104] (4) Preparation of Surface-Protected Fiber-Reinforced Composite Material Eight composite material precursors described in (7) of <Materials Used in Examples and Comparative Examples> were stacked in a quasi-isotropic manner (stacking configuration: [+45° / 0° / -45° / 90°]). ｓ ) to be used as the protection target, and the resin surface of the surface protection material prepared in (3) was attached to the outermost surface of the target to form a surface-protection-material-attached fiber-reinforced composite material precursor. This precursor was then cured in an autoclave under conditions of 6 atmospheres, 180°C for 2 hours, and a temperature increase rate of 1.7°C / min to obtain a surface-protected fiber-reinforced composite material.

[0105] <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.

[0106] (1) Flow Index of Epoxy Resin Composition The epoxy resin composition was extracted from the surface protective material prepared by the method described above in the section "Epoxy Resin Composition," in which the surface protective material was sandwiched between release papers and heated and compressed with an iron, and the flow index was evaluated.

[0107] To calculate the flow index of an epoxy resin composition, first, the complex viscosity of the resin composition was measured using an ARES-G2 dynamic viscoelasticity analyzer (manufactured by TA Instruments Inc.). Flat parallel plates with a diameter of 25 mm were used as upper and lower measuring jigs, and the epoxy resin composition was placed between the upper and lower jigs so that the distance between the upper and lower jigs was 1 mm. The complex viscosity was then measured in a torsion mode (measurement frequency: 1 Hz) while the temperature was raised from 20°C to 100°C at a rate of 5°C / min to obtain continuous values ​​over the temperature range. The reciprocal of the complex viscosity was then integrated over the range of 20 to 100°C to calculate the flow index (1 / Pa s).

[0108] (2) Amount of Resin in Composite Material Precursor Exposed on the Surface The surface-protected fiber-reinforced composite material was subjected to IR measurement by the ATR method on the side where the surface protection material was provided. The measurement was performed using an FT / IR-4000 manufactured by JASCO Corporation (prism: diamond, measurement wavelength: 400 to 4,000 cm). －１ , cumulative number: 16). －１ The peak at 1,592 cm, which indicates the benzene ring derived from the cured resin used in the composite material precursor, was normalized using the peak at 1,592 cm －１ The peak value of the peak value was determined and evaluated as the amount of resin of the composite material precursor exposed on the surface of the surface-protected fiber composite material due to the mixing phenomenon (hereinafter abbreviated as the exposed resin amount, unit: dimensionless). The smaller the exposed resin amount, the more excellent the light resistance of the surface-protected fiber-reinforced composite material.

[0109] (3) Handleability of Surface Protective Material The handleability of the surface protective material was evaluated as follows. (i) When the epoxy resin composition was not transferred from the surface protective material to the rubber gloves when handling the surface protective material, the resin transfer in the handleability of the surface protective material was rated as "good". (ii) A 10 cm square surface protective material was completely fixed at the center of one side with a clip and hung from above, and a 0.5 kg weight was hung at the center of the opposite side facing downward. When a load was applied to the surface protective material, if no distortion occurred in the surface protective material, it was rated as "very good". If the elongation in the hanging direction of the weight was 3 cm or less, the distortion was rated as "good", and if it was more than that, it was rated as "poor". (iii) In the above (ii), the weight was changed to 1.0 kg. If there were no defects in the surface protective material, it was rated as "very good". If partial tearing was observed, it was rated as "good", and if it was completely torn, it was rated as "poor".

[0110] (4) Measurement of gaps in fiber substrates The fiber substrate was cut into 10 cm x 10 cm squares to prepare samples, and an observation image of one arbitrary portion of the sample was obtained at 100x magnification using an optical microscope (VHX-5000 (manufactured by Keyence Corporation)) in a state where the fiber substrate portion and gap portion could be easily distinguished (the fiber substrate was attached to drawing paper of a different color from the fiber substrate). The obtained observation image was binarized using ImageJ / Fiji to distinguish the gap portion and the fiber substrate portion, and the gap (%) was calculated by determining the ratio of the area of ​​the gap portion to the total area of ​​the observation image. The gaps were measured for each of five fiber substrates cut into 10 cm x 10 cm squares at arbitrary positions, and the average value was used. <Examples 1 to 8> In Examples 1 to 4, surface protection materials were prepared using epoxy resin compositions of similar composition but with different types of fiber substrates. Nonwoven fabric substrates having different surface areas were used in Examples 1 and 2, and woven fabrics having different surface areas were used in Examples 3 and 4. Examples 1 to 4 showed that the mixing phenomenon can be further suppressed by using a fibrous substrate with a large surface area in both the nonwoven fabric substrate and the woven fabric.

[0111] Furthermore, in terms of the handleability of the surface protective materials, the surface protective materials using the nonwoven fabric substrates of Examples 1 and 2 showed extremely good distortion in terms of handleability, and the surface protective materials using the woven fabric of Examples 3 and 4 showed extremely good tear resistance.

[0112] In Examples 5 to 8, surface protective materials were prepared using epoxy resin compositions of similar composition but with different fiber substrates. However, in Examples 5 to 8, epoxy resin compositions with lower flow indexes were used than those used in Examples 1 to 4. In this case, comparing Examples 5 to 8 with Examples 1 to 4 using the same fiber substrate (e.g., Example 1 compared with Example 5), it was found that Examples 5 to 8, which used epoxy resin compositions with lower flow indexes, suppressed the mixing phenomenon. <Examples 1, 3, 9, and 10> In Examples 9 and 10, component [B] was removed from the epoxy resin composition used in Example 1, and a surface protective material was prepared using an epoxy resin composition with a significantly higher flow index. The combinations that share the same fiber substrate are the combination of Example 9 with Example 1, and the combination of Example 10 with Example 3. In Examples 9 and 10, the amount of resin in the composite material precursor exposed on the surface due to the mixing phenomenon was higher than in the corresponding Examples 1 and 3. Although both were at a level that made them usable as surface protective materials, the resin transfer and other properties were poor, as shown in the table. Example 1, Comparative Examples 1 to 4 In Comparative Example 1, the same evaluation was carried out using the resin composition prepared in Example 1, but using a resin film that did not contain a fibrous substrate. The resin film alone lost its shape and was difficult to handle.

[0113] In Comparative Example 2, the resin basis weight was lower than that in Example 1, and the surface area of ​​the fiber substrate × the thickness of the surface protective material (×10 －６ (m ２ ・m) / m ２ As a result, a large amount of resin was exposed.

[0114] In Comparative Example 3, a nonwoven fabric substrate having a smaller surface area of ​​the fiber substrate was used compared to Example 1. As a result, a larger amount of resin was exposed.

[0115] In the above-described Examples and Comparative Examples 1 to 3, the quality of the resin films was good, but in Comparative Example 4, film formation using a knife coater was attempted, but a large number of streaky areas where the epoxy resin was not applied occurred, making it impossible to produce a resin film of good quality. <Examples 1 to 4, Comparative Example 1, Examples 11 to 18> In Examples 11 and 13, the resin basis weight was changed based on Example 2, and in Examples 12 and 14, the resin basis weight was changed based on Example 4. In a surface protective material using the same epoxy resin composition and a fiber substrate, an increase in the resin basis weight increased the surface area of ​​the fiber substrate × the thickness of the surface protective material (×10 －６ (m ２ ・m) / m ２ ) value improved, resulting in less exposed resin.

[0116] In Examples 15 and 16, different types of nonwoven fabric substrates were used compared to Examples 1 and 2 and Comparative Example 1, and in Examples 17 and 18, different types of woven fabrics were used compared to Examples 3 and 4. For the same resin composition and resin basis weight, the surface area (m ２ / m ２ ), surface area of ​​fiber substrate × thickness of surface protection material (×10 －６ (m ２ ・m) / m ２ By using a fiber substrate with a large flow index and few gaps, the amount of exposed resin was reduced. <Examples 2, 4, 6, 8, Examples 19 to 28> In Examples 19, 21, 23, and 25, the type of component [B] was changed based on Example 2, and in Examples 20, 22, 24, and 26, the type of component [B] was changed based on Example 4. Although the blending amounts were the same, the flow index varied depending on the type of thixotropic agent. When comparing surface protection materials using the same fiber substrate, the amount of exposed resin was reduced by using an epoxy resin composition with a low flow index.

[0117] In Example 27, the amount of component [D] was changed based on Example 2, and in Example 28, the amount was changed based on Example 4. When Example 27 is compared with Examples 2 and 6, and Example 28 is compared with Examples 4 and 8, the flow index decreased and the amount of exposed resin was reduced due to the increased amount of component [D]. <Examples 1 to 2, 4, 15 to 16, Examples 29 to 37> In Examples 29 and 31, the amount of component [B] was changed based on Example 2, and in Examples 30 and 32, the amount was changed based on Example 4. The increase in the amount of thixotropic agent decreased the flow index and the amount of exposed resin was reduced.

[0118] In Examples 33 and 35, the type of component [A] and the type of component [C] were changed based on Example 2, and in Examples 34 and 36, the type of component [A] and the type of component [C] were changed based on Example 4. When the type of component [A] was changed from Celloxide 2021P to EPALLOY 5000, the flow index increased and a large amount of exposed resin was produced. When the type of component [C] was changed from San-Aid SI-100 to jER Cure DICY7 and a curing accelerator was added, the flow index increased and a large amount of exposed resin was produced.

[0119] In Example 37, a nonwoven fabric substrate made of PET fiber was used. Compared with Examples 1 to 2 and 15 to 16, which used a nonwoven fabric substrate made of glass fiber but had the same epoxy resin composition and resin basis weight, a larger amount of resin was exposed.

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[0126] REFERENCE SIGNS LIST 1: Fiber substrate 2: Epoxy resin composition 3: Surface protective material 4: Fiber surface 5: Resin surface

Claims

1. A surface protection material obtained by impregnating a fiber substrate with an epoxy resin composition containing components [A], [D], and [C], wherein the surface area of ​​the fiber substrate per unit area is 2.0 to 30 (m ２ / m ２ ), and the value obtained by multiplying the surface area of ​​the fiber substrate per unit area by the thickness of the surface protection material is 150 to 2000 (× 10 －６ (m ２ ・m) / m ２ [A] non-aromatic epoxy resin [D] non-aromatic thermoplastic resin [C] hardener 2. The flow index of the epoxy resin composition is 0.05 to 1.5 (Pa·s). －１ The surface protective material according to claim 1 , 3. The surface protective material according to claim 1 or 2, wherein the voids of the fiber substrate are 3 to 35%.

4. The surface protective material according to claim 1 or 2, wherein the curing agent [C] is a cationic curing agent or an anionic curing agent.

5. The surface protective material according to claim 1 or 2, wherein the fiber substrate comprises glass fiber.

6. The surface protective material according to claim 1 or 2, wherein the fiber substrate has the form of a nonwoven fabric substrate or a woven fabric.

7. The surface protective material according to claim 6, wherein the fiber substrate has the form of a nonwoven fabric substrate, and the porosity of the fiber substrate is 3 to 35%.

8. The surface protective material according to claim 6, wherein the fiber substrate has a woven fabric form and the porosity of the fiber substrate is 3 to 25%.

9. The fiber substrate has the form of a nonwoven fabric substrate, and the surface area of ​​the fiber substrate is 2.0 to 7.0 (m ２ / m ２ The surface protective material according to claim 6, wherein 10. The fiber substrate has a woven fabric form, and the surface area of ​​the fiber substrate is 3.0 to 30 (m ２ / m ２ The surface protective material according to claim 6, wherein 11. The surface protective material according to claim 6, wherein the fiber substrate has the form of a woven fabric, and the number of fibers constituting the yarn bundles in the warp direction and fill direction is 20 to 80.

12. A surface molding obtained by curing the surface protective material according to claim 1 or 2 or a laminate of a plurality of said surface protective materials.

13. 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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