Slit tape prepreg

Abstract

By defining the surface condition of the slit tape prepreg, the amount of adhesion to the AFP thread guide is reduced while providing a slit tape prepreg that exhibits good adhesion to the laminated substrate. [Solution] A slit tape prepreg obtained by impregnating carbon fibers with an epoxy resin composition, wherein the coating layer localized on the outside of the carbon fiber layer on at least one surface of the slit tape prepreg satisfies the following conditions: [a] the coating layer contains a liquid resin and particles insoluble in the liquid resin; [b] the average thickness of the coating layer is 1 μm or more and 14 μm or less; and [c] the average line roughness (arithmetic mean height Ra) of the surface of the coating layer is 2 μm or more and 10 μm or less.

Description

Technical Field

[0001] The present invention relates to a slit tape prepreg obtained by impregnating carbon fibers with an epoxy resin composition. Background Art

[0002] Fiber-reinforced composite materials (FRP) using reinforcing fibers such as carbon fibers, aramid fibers, and glass fibers are utilized as structural materials for aircraft, automobiles, sporting goods, and materials for general industrial applications by taking advantage of their high specific strength and specific modulus of elasticity. Particularly in the aircraft industry, they are widely used for the purpose of saving fuel and reducing operating costs, and especially for load-bearing structural materials, fiber-reinforced composite materials obtained by curing and molding prepregs, which are intermediate base materials obtained by impregnating aligned reinforcing fibers with a matrix resin, are commonly used.

[0003] Automatic Fiber Placement (AFP) technology is utilized in the manufacturing of aircraft members made of fiber-reinforced composite materials. AFP technology is a technology for automatically placing and laminating narrow-width prepregs composed of fibers and resin at appropriate positions. In an AFP apparatus, a laminated base material made of prepregs can be manufactured by automatically repeating the lamination of prepregs.

[0004] As a material to be laminated by AFP technology, a slit tape prepreg obtained by slitting a prepreg in the fiber direction and winding it into a tape shape is used. In the lamination process of slit tape prepregs by AFP technology (hereinafter referred to as the AFP lamination process), the slit tape prepreg is unwound from the creel stand of the AFP apparatus, supplied to the lamination head section, passes through the yarn path guide inside the lamination head, and is attached and laminated by a nip roll onto a laminated base material made of slit tape prepregs that has already been laminated. At this time, the laminated base material of the slit tape prepreg is heated by a heater provided in the lamination head section, the resin on the surface of the base material softens, and tackiness (adhesiveness) is developed.

[0005] In the AFP lamination process, when the slit tape prepreg passes through the thread guide, the thread guide and the slit tape come into contact, causing friction. At this time, resin adheres to the thread guide, and unimpregnated fibers contained in the slit tape that passes through subsequently accumulate, which can generate clumps of resin and fluff (hereinafter referred to as resin fluff deposits). If resin fluff deposits accumulate in the lamination head, they can clog the slit tape prepreg supply section or cause the slit tape to wrap around the nip roll due to the resin fluff deposits, leading to problems that can cause the equipment to stop.

[0006] In response to this, an approach is sometimes taken to reduce tackiness by adjusting the viscoelasticity of the slit tape surface resin at room temperature and when heated, in order to prevent resin from adhering to the AFP device. However, if the viscosity of the slit tape surface resin becomes excessively high, untack occurs during the AFP lamination process, leading to equipment trouble. Untack refers to the phenomenon in which the slit tape does not exhibit sufficient tackiness and lifts up without adhering to the laminated substrate during lamination. In other words, adjusting only the viscoelasticity of the slit tape surface resin results in a trade-off between resin fuzz adhesion to the thread guide and adhesion during lamination.

[0007] To avoid this problem, measures have been taken from a process perspective using AFP equipment, such as adjusting the temperature of the slit tape when it passes through the thread guide and at the nip stage. However, the materials used for slit tapes for fiber-reinforced composite materials have many constraints in terms of mechanical properties and heat resistance, and it has been conventionally difficult to make the material itself exhibit excellent AFP process passability.

[0008] Patent Document 1 discloses a slit tape that improves passability through the AFP process by defining the composition of the thermoplastic resin in the prepreg and significantly lowering the storage modulus at 40°C compared to the storage modulus at 25°C of the surface resin, thereby suppressing resin adhesion to the guide while maintaining adhesion during lamination.

[0009] Patent Document 2 discloses a prepreg that exhibits excellent process passability not only when passing through the guide of the AFP device but also in the slitting process when the prepreg is converted into slit tape, by defining the impregnation rate of the prepreg and the loss tangent (tanδ) of the matrix resin measured by the WPU (water pickup) method. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] International Publication No. 2018 / 135594 [Patent Document 2] International Publication No. 2021 / 200453 [Overview of the project] [Problems that the invention aims to solve]

[0011] Although the slit tape described in Patent Document 1 has excellent handling properties at room temperature or below, its tackiness is still low, and its tackiness during lamination is not sufficient.

[0012] Patent Document 2 specifies only the impregnation rate of the slit tape, without mentioning the amount of surface resin, which presented challenges in terms of tackiness and splice strength. Generally, the impregnation rate measured by the WPU method quantifies the amount of water immersed in the voids inside the slit tape, and the amount of surface resin required a separate evaluation.

[0013] The objective of the present invention is to provide a slit tape prepreg that can achieve both excellent AFP process passability, i.e., suppression of resin and fluff adhesion to the thread guide, and tackiness during lamination. [Means for solving the problem]

[0014] To solve these problems, the present invention employs the following means.

[0015] [1] A slit tape prepreg formed by impregnating carbon fibers with an epoxy resin composition, wherein the slit tape prepreg has a coating layer satisfying the following [a] to [c] on at least one surface layer of the slit tape prepreg. [a] the coating layer comprises a liquid resin and particles insoluble in said liquid resin [b] an average thickness of the coating layer is 1 µm or more and 14 µm or less [c] an average line roughness (arithmetic mean height Ra) of a surface of the coating layer is 2 µm or more and 10 µm or less [2] The slit tape prepreg according to [1], wherein a surface coverage of the coating layer is 65% or more and 95% or less with respect to a surface of the slit tape prepreg. Effects of the Invention

[0016] By using the slit tape of the present invention, it is possible to provide a slit tape prepreg that achieves both excellent AFP process passability, that is, suppression of resin fluff adhesion to yarn path guides, and tackiness during lamination. Brief Description of the Drawings

[0017] [Figure 1] It is a schematic cross-sectional view of a surface of a slit tape prepreg. [Figure 2] It is a schematic diagram of a method for producing a slit tape. [Figure 3] It is a schematic diagram of a simple evaluation apparatus for AFP process passability and laminating properties. Mode for Carrying Out the Invention

[0018] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[0019] The present invention is a slit tape prepreg formed by impregnating carbon fibers with an epoxy resin composition, wherein the slit tape prepreg has a coating layer satisfying the following [a] to [c] on at least one surface layer of the slit tape prepreg. [a] the coating layer comprises a liquid resin and particles insoluble in said liquid resin (b) the average thickness of the coating layer is 1 µm or more and 14 µm or less (c) the average line roughness (arithmetic mean height Ra) of the surface of the coating layer is 2 µm or more and 10 µm or less

[0020] Carbon fibers are used in the slit tape prepreg of the present invention from the viewpoint of obtaining a lightweight and highly rigid fiber-reinforced composite material. Examples of the carbon fibers include polyacrylonitrile-based, pitch-based and other carbon fibers, and polyacrylonitrile-based carbon fibers (PAN) having high tensile strength are particularly preferable. It is preferable that the carbon fibers used have a number of filaments in one fiber bundle ranging from 1,000 to 50,000. If the number of filaments is less than 1,000, the fiber arrangement tends to meander, which may cause a decrease in strength. From the viewpoint of being particularly suitable for aerospace applications, the lower limit of the number of filaments is more preferably 2,500 or more, and the upper limit is more preferably 40,000 or less.

[0021] Furthermore, an epoxy resin composition is used as the matrix resin in the slit tape prepreg of the present invention. When the epoxy resin composition is used, it can be heated to exhibit appropriate tackiness during the AFP lamination process, and the composite obtained by curing the slit tape laminate can exhibit high mechanical properties. Here, the epoxy resin composition refers to a mixture containing an epoxy resin main agent and a curing agent as essential components, and may contain a thermoplastic resin component, particles, and other curing accelerators as additives as needed.

[0022] In the slit tape prepreg of the present invention, it is important that in addition to being impregnated into the carbon fibers, the epoxy resin composition exists as an epoxy resin composition localized on the outer side of the carbon fiber layer 11 (the surface 1 of the slit tape prepreg), that is, as the coating layer 12, as shown in Figure 1.

[0023] It is important that the coating layer 12 satisfies the following (a) to (c). (a) the coating layer comprises a liquid resin and particles insoluble in the liquid resin (b) the average thickness of the coating layer is 1 µm or more and 14 µm or less [c] The average surface roughness (arithmetic mean height Ra) of the coating layer is 2 μm or more and 10 μm or less.

[0024] Regarding [a], it is important that the coating layer 12 contains liquid resin. By including liquid resin, the laminated substrate of the slit tape prepreg is heated during the AFP lamination process, which reduces the viscosity of the liquid resin on the surface, allowing sufficient tackiness to be achieved when the layers adhere during lamination.

[0025] Furthermore, it is important that the coating layer 12 contains particles 15 that are insoluble with the liquid resin. By including the particles 15, the slit tape prepreg can have an uneven surface, which reduces the contact area between the guide and the slit tape prepreg when it passes through the thread guide section of the AFP device, thereby suppressing the adhesion of resin fluff.

[0026] Here, it is preferable that the particles 15 are present in greater quantities in the coating layer 12 than in the epoxy resin composition impregnated within the carbon fibers. By localizing the particles 15 in the coating layer 12, more irregularities can be expressed on the surface of the slit tape prepreg. Furthermore, in the cured fiber-reinforced composite material, the spaces between the carbon fiber layers are strengthened, and a fiber-reinforced composite material with excellent impact resistance can be obtained.

[0027] In the present invention, the average particle diameter is preferably 8 to 20 μm, and more preferably 10 to 15 μm. When the flat particle diameter is 8 to 20 μm, the surface of the slit tape prepreg has irregularities, which suppresses resin adhesion to the AFP device guide section, allows for the development of appropriate tackiness during lamination, and further allows for the creation of a fiber-reinforced composite material with excellent impact resistance after curing. In addition, because the particles are larger than 8 μm, they do not penetrate into the carbon fiber layer, the particles are localized in the coating layer 12, and irregularities can be created on the surface of the slit tape prepreg.

[0028] It is preferable to use thermoplastic resin particles for particle 15. By using thermoplastic resin particles, a fiber-reinforced composite material with excellent interlaminar toughness can be obtained by laminating and curing the slit tape prepreg. Here, being insoluble in the epoxy resin composition means that in an epoxy resin composition in which particle 15 is dispersed, the particles do not substantially dissolve in the epoxy resin composition. For example, this refers to a state in which, using a transmission electron microscope, the particles in the epoxy resin composition can be observed with a clear interface between the particles and the matrix resin without substantially shrinking from their original size.

[0029] As particle 15, a thermoplastic resin obtained by mixing with an epoxy resin composition can be used. Among these, polyamide is most preferred, and among polyamides, nylon 12, nylon 6, nylon 11, nylon 66, and nylon 6 / 12 copolymers provide particularly good adhesive strength with epoxy resin. The shape of these thermoplastic resin particles may be spherical, non-spherical, or porous. Commercially available polyamide particles include "Trepearl" (registered trademark) TN (manufactured by Toray Industries, Inc., average particle diameter: 13.0 μm) and "SP-10" (registered trademark) (manufactured by Toray Industries, Inc., average particle diameter: 12.0 μm). These polyamide particles may be used alone or in combination of multiple types.

[0030] In the present invention, the particles 15 are preferably present in an amount of 0.1 to 30% by mass relative to the epoxy resin composition, more preferably 1 to 25% by mass, and even more preferably 5 to 20% by mass. When the particles 15 are present in an amount of 0.1 to 30% by mass relative to the epoxy resin composition in the coating layer 12, a fiber-reinforced composite material with excellent impact resistance can be obtained, and resin adhesion to the thread guide during the AFP lamination process can be suppressed.

[0031] Regarding [b], it is important that the average thickness of the coating layer 12 is 1 μm or more and 14 μm or less, and more preferably 6 μm or more and 12 μm or less. The average resin thickness of the coating layer 12 refers to the average thickness (17 in Figure 1) of the epoxy resin composition localized outside the outermost surface 13 of the carbon fiber layer at any position on the slit tape prepreg, and can be measured with a laser microscope by the method described later.

[0032] When the thickness exceeds 1 μm, the coating layer 12 acts as an adhesive layer during lamination, providing appropriate tackiness to the slit tape prepreg and suppressing the occurrence of untack during the AFP lamination process. On the other hand, if the average thickness of the coating layer 12 exceeds 14 μm, the resin tends to adhere excessively to the thread guide, making it impossible to suppress the adhesion of resin fluff as it passes through the thread guide.

[0033] Regarding [c], it is important that the average line roughness (arithmetic mean height Ra) of the surface of the coating layer is 2 μm or more and 10 μm or less, more preferably 3 μm or more and 7 μm or less. Here, the line roughness Ra is defined as the arithmetic mean roughness of the roughness curve between two points 0.1 mm apart in the longitudinal direction when viewing the slit tape prepreg from directly above on the surface 16 of the coating layer 12 at any position on the slit tape prepreg, and the average of the line roughness measured at five locations is taken as the average line roughness. The line roughness can also be measured with a laser microscope by the method described later. Because the surface of the coating layer is not smooth but has irregularities, and the average line roughness Ra is 2 μm or more, the slit tape prepreg can reduce the contact area with the thread guide during the AFP lamination process and suppress the adhesion of resin lint.

[0034] As mentioned above, the coating layer 12 can have surface irregularities by containing liquid resin and particles. In this case, if the average line roughness Ra of the coating layer 12 containing liquid resin and particles is 2 μm or more, the contact area with the thread guide can be reduced during the AFP lamination process, and resin fluff adhesion can be suppressed. Furthermore, if the average line roughness Ra is 10 μm or less, when the coating layer 12 is heated and deformed during lamination, a sufficient bonding area can be secured for bonding between the substrates, and lamination can be performed without untack.

[0035] Therefore, the average linear roughness (arithmetic height Ra) of the surface roughness of the coating layer must be 2 to 10 μm or less, and only by simultaneously satisfying the characteristics of [a], [b], and [c] can the slit tape prepreg achieve both "suppression of resin and fluff adhesion to the thread guide section" and "suppression of untack" in the AFP lamination process, which are mutually contradictory.

[0036] In the slit prepreg tape of the present invention, the surface resin coverage rate of the coating layer 12 is preferably 65% ​​or more and 95% or less. Here, the surface resin coverage rate refers to the area ratio of the projected surface surface 16 of the coating layer 12 to the projected surface surface of the slit tape prepreg at any position when the slit tape prepreg is viewed from directly above, and can be measured with a laser microscope by the method described later. A surface resin coverage rate of 65% or more allows the coating layer to exhibit sufficient tackiness when heated and deformed during lamination, enabling adhesion between the surfaces of the slit tape prepregs. Furthermore, a surface resin coverage rate of 95% or less reduces the contact area with the thread guide during the AFP lamination process, suppressing the adhesion of resin fluff.

[0037] The average thickness of the coating layer 12 can be measured using a laser microscope in the following way: Using a 10x objective lens, the surface of the slit tape prepreg is placed in a field of view of 1.0 mm × 1.4 mm, and the focus is set in the height direction of the surface 16 of the coating layer 12 in Figure 1. The point of focus in the height direction is taken as the center in the height direction, and the focal position is moved in the height direction every 2.5 μm within a range of 0.2 mm (0.1 mm above and below the center) to acquire images of the slit tape prepreg surface. Subsequently, depth stacking is performed on each acquired image to create 3D data of the slit tape prepreg surface. In the slit tape prepreg surface image viewed from directly above, two exposed parts 14 of the coating layer 12 are selected, and the ends of these two parts are connected by lines, and a cross-sectional curve of the surface 16 of the coating layer is obtained based on the 3D data. From the obtained cross-sectional curve, the average height 18 of the surface 16 of the coating layer 12 is measured using laser microscope analysis software. On the other hand, by measuring the average height of two ends of the cross-sectional curve, i.e., the exposed portion 14 of the coating layer 12, the average height 19 of the coating layer 12 and its interface 13 is calculated. The thickness 17 of the coating layer 12 can be calculated by calculating the difference between the average height 18 of the cross-sectional curve and the average height 19 of the interface 13. The average thickness of the coating layer 12 can be calculated by repeating the same operation at 15 locations on the surface of the slit tape prepreg and calculating the average value.

[0038] The surface roughness of the coating layer 12 can be measured using a laser microscope in the following way: Using a 50x objective lens, the slit tape prepreg surface is positioned within a field of view of 0.2 mm × 0.28 mm. At this time, the horizontal direction relative to the field of view is aligned with the longitudinal direction of the slit tape prepreg. An arbitrary point in the height direction of the surface 16 of the coating layer 12 in Figure 1 is defined as the center in the height direction, and images of the slit tape prepreg surface are acquired by moving the focal position in 0.1 μm increments within a range of 0.06 mm (0.03 mm above and below the center). Depth stacking is performed on these images to create 3D data of the slit tape prepreg surface. Next, in the surface image of the 3D data viewed from directly above, a line with a length of 0.1 mm is drawn horizontally at an arbitrary position on the surface 16 of the coating layer 12, and a cross-sectional curve of the surface 16 of the coating layer 12 is obtained based on the 3D data. The surface roughness Ra is measured from the cross-sectional curve using laser microscope analysis software. By repeating this process five times and calculating the average value, the surface roughness of the coating layer 12 can be calculated.

[0039] Furthermore, the outermost surface 13 of the carbon fiber layer 11 on the surface of the slit tape prepreg can be observed from directly above with a laser microscope, as described later, in the exposed portion 14 of the carbon fiber layer 11 that is not covered by the coating layer 12 on the surface of the slit tape. The outermost surface of the carbon fiber layer 11 in the portion other than the exposed portion 14, that is, the interface 13 between the coating layer 12 and the internal epoxy resin composition-impregnated carbon fiber layer 11, is defined by a plane connecting the ends of the exposed portion 14.

[0040] The slit tape prepreg of the present invention must be wide enough to be introduced into an AFP device. Examples of widths include 38.1 mm (1.5 inches), 25.4 mm (1 inch), 12.7 mm (1 / 2 inch), 6.35 mm (1 / 4 inch), and 3.175 mm (1 / 8 inch).

[0041] The surface resin coverage rate of the coating layer 12 can be measured using a laser microscope in the following way. Three-dimensional data of the slit tape prepreg surface is prepared in the same manner as the average thickness acquisition method described above. In the obtained three-dimensional data, the exposed portions 14 of the carbon fiber layer where the carbon fiber layer 11 is not covered by the coating layer 12 are marked in the slit tape prepreg surface image viewed from directly above. The ratio of the total area (projected area) of the exposed portions 14 to the total projected area of ​​the slit tape prepreg surface image is calculated by image analysis and is defined as the percentage of exposed carbon fiber layer (%). The surface resin coverage rate can be calculated as 100 - percentage of exposed carbon fiber layer (%). [Examples]

[0042] The present invention will be described in detail below with reference to examples. However, the scope of the present invention is not limited to these examples. Furthermore, unless otherwise noted, the various characteristics were measured under conditions of 23°C and 50% relative humidity.

[0043] (1) Slit tape prepreg material A bobbin of narrow tape (6.35 mm wide) made from Toray Industries, Inc.'s prepreg "T800S / 3900-2" was prepared. However, this material is merely an example of a preferred embodiment of the present invention, and the present invention is not limited to these materials.

[0044] (2) Method for manufacturing slit tape prepregs Figure 2 shows the method for manufacturing the slit tape of the present invention. A slit tape prepreg processing device 2 was manufactured to produce the slit tape prepreg. The T800S / 3900-2 slit tape prepreg 21, wound on a paper tube, was unwound while peeling it from the release film 22, and then passed through a heating section 25 while being heated with an IR heater. After that, the slit tape prepreg and the release film 22 were wound back onto the paper tube to produce the processed slit tape prepreg 26. At this time, the heating temperature and running speed when passing through the heating section were adjusted as necessary so that the average thickness of the coating layer, surface roughness, and surface resin coating rate of the slit tape prepreg were to be the values ​​shown in Table 1.

[0045] (3) Method for measuring coating layer thickness and surface resin coverage The obtained slit tape prepreg was cut at an arbitrary position, and the surface of the slit tape prepreg was observed using a laser microscope (VK-X3000 (manufactured by Keyence Corporation)). At this time, a 10x objective lens was used, and the observation was performed within a field of view of 1.0 mm × 1.4 mm. The focal point in the height direction of the surface 16 of the coating layer in Figure 1 was set to the center in the height direction, and the focal position was moved in the height direction in 2.5 μm increments within a range of 0.2 mm, 0.1 mm above and below the center, to acquire images of the slit tape prepreg surface. Depth stacking was performed to create 3D data of the slit tape prepreg surface. In the slit tape prepreg surface image viewed from directly above, two exposed portions 14 of the carbon fiber layer were selected, and the ends of these two locations were connected by lines. Based on the 3D data, a cross-sectional curve of the surface 16 of the coating layer was obtained. From the obtained cross-sectional curve, the average height 18 of the surface 16 was measured using laser microscope analysis software, while the average height 19 of the interface 13 between the carbon fiber layer and the coating layer was calculated by measuring the average height of two points at the ends of the cross-sectional curve, i.e., the exposed portions 14 of the carbon fiber layer. The thickness 17 of the coating layer was calculated by calculating the difference between the average height of the cross-sectional curve and the average height of the interface 13. The same operation was repeated at 15 points on the surface of the slit tape prepreg, and the average value was calculated to determine the average thickness of the coating layer 12. Furthermore, in the obtained 3D data of the slit tape prepreg surface image viewed from directly above, the exposed portions 14 of the carbon fiber layer where the carbon fiber layer 11 was not covered by the coating layer 12 were marked. The ratio of the total area (projected area) of the exposed portions 14 to the projected area of ​​the surface image of the slit tape prepreg was calculated by image analysis and was defined as the percentage of exposed carbon fiber layer. The surface resin coating rate was calculated as 100 - percentage of exposed carbon fiber layer.

[0046] (4) Method for measuring surface roughness of slit tape The obtained slit tape prepreg was cut at an arbitrary position, and the surface of the slit tape prepreg was observed using a laser microscope (VK-X3000 (manufactured by Keyence Corporation)). At this time, a 50x objective lens was used to observe within a field of view of 0.2 mm × 0.28 mm, and the microscope was positioned so that the horizontal direction relative to the field of view was the longitudinal direction of the slit tape prepreg. An arbitrary point in the height direction of the surface 16 of the coating layer in Figure 1 was defined as the center in the height direction, and images of the slit tape prepreg surface were acquired by moving the focal position in the height direction in 0.1 μm increments within a range of 0.06 mm (0.03 mm above and below the center). Depth stacking was performed on these images to create 3D data of the slit tape prepreg surface. Next, in the surface image of the 3D data viewed from directly above, a line with a length of 0.1 mm was drawn horizontally at an arbitrary position on the surface 16 of the coating layer, and a cross-sectional curve of the surface 16 of the coating layer was obtained based on the 3D data. From the cross-sectional curve, the surface roughness Ra was measured using laser microscope analysis software. By repeating this process five times and calculating the average value, the surface roughness of the coating layer 12 was determined.

[0047] (5) Method for evaluating the passability of slit tape prepregs through the AFP process To evaluate the AFP processability of the obtained slit tape prepreg, a simplified AFP lamination evaluation device 3 was fabricated and used to perform automatic lamination with feeding, cutting, heating, and bonding of the slit tape prepreg, as shown in Figure 3. The lamination was performed at a lamination speed of 0.5 m / sec so that a total of 1000 m of slit tape was bonded onto a pre-laminated slit tape prepreg laminate substrate 31. Cutting and feeding at the cutting section 41 were repeated every 1 m of slit tape. The evaluation was performed in a constant temperature and humidity chamber 39 (TBR-4E20 manufactured by ESPEC Corporation), with the ambient temperature set to 15°C. In addition, the surface temperature of the already laminated slit tape 37 beneath the slit tape 22 being laminated, which was in contact with the nip roll 34, was heated with an IR heater 35 to 40°C, and the surface temperature of the laminated section was monitored with a thermograph 36 (E4 manufactured by FLIR Corporation). Process passability within the AFP apparatus was evaluated on a four-point scale (S, A, B, C) based on the following indicators. Furthermore, the worse of the two evaluation results (thread guide resin adhesion amount and lamination untack occurrence) was used as the overall judgment for "AFP process passability and lamination performance." The results are shown in Table 1.

[0048] <Amount of resin lint adhering to the thread guide> The amount of resin fluff adhering to the thread guide was defined as the weight of the thread guide after a 1000m lamination test minus the weight of the thread guide before the lamination test. A thread guide with less than 5mg of resin adhering was evaluated as "S", 10mg or less as "A", 50mg or less as "B", and more than 50mg as "C".

[0049] <Evaluation of untack generation during stacking> Untack was defined as a state where the slit tape was lifted up to a height of 5 mm or more at the point where it was most detached from the laminated substrate, or a state where the slit tape was not adhered to the laminated substrate at all. The amount of lifting was monitored using a length measuring sensor 38 located 300 mm away from the nip roll 24. The number of untack occurrences in a 1000 m lamination was evaluated as "S" if it was 1 or less, "A" if it was 5 or less, "B" if it was 10 or less, and "C" if it was more than 10.

[0050] (Example 1) A processed slit tape prepreg was prepared according to the above-mentioned "(1) Slit tape prepreg material (2) Method for preparing slit tape prepreg". Subsequently, the prepared slit tape prepreg was evaluated according to the above-mentioned "(3) Method for measuring the thickness of the coating layer and the surface resin coverage rate of the slit tape (4) Method for measuring the surface roughness of the slit tape". The average thickness of the surface resin epoxy resin composition layer was 10.0 μm, the surface roughness Ra was 3.5 μm, and the surface resin coverage rate was 70%. Furthermore, using the prepared slit tape prepreg, the AFP processability was evaluated according to the above-mentioned "(5) Evaluation of the passability of the slit tape prepreg in the AFP process". The amount of thread guide resin adhesion was "S", the evaluation of untack occurrence during lamination was "S", and the overall judgment result for passability in the AFP process and laminationability was "S".

[0051] (Example 2) A processed slit tape prepreg was prepared according to the above-described "(1) Slit tape prepreg material (2) Method for preparing slit tape prepreg". Subsequently, the prepared slit tape prepreg was evaluated according to the above-described "(3) Method for measuring the thickness of the coating layer and the surface resin coverage rate of the slit tape (4) Method for measuring the surface roughness of the slit tape". The average thickness of the surface resin epoxy resin composition layer was 6.0 μm, the surface roughness Ra was 6.9 μm, and the surface resin coverage rate was 64%. Furthermore, using the prepared slit tape prepreg, the AFP processability was evaluated according to the above-described "(5) Evaluation of the passability of the slit tape prepreg in the AFP process". The amount of thread guide resin adhesion was "S", the evaluation of untack occurrence during lamination was "A", and the overall judgment result for passability in the AFP process and laminationability was "A".

[0052] (Example 3) A processed slit tape prepreg was prepared according to the above-mentioned "(1) Slit tape prepreg material (2) Method for preparing slit tape prepreg". Subsequently, the prepared slit tape prepreg was evaluated according to the above-mentioned "(3) Method for measuring the thickness of the coating layer and the surface resin coverage rate of the slit tape (4) Method for measuring the surface roughness of the slit tape". The average thickness of the surface resin epoxy resin composition layer was 9.2 μm, the surface roughness Ra was 2.5 μm, and the surface resin coverage rate was 96%. Furthermore, using the prepared slit tape prepreg, the AFP processability was evaluated according to the above-mentioned "(5) Evaluation of the passability of the slit tape prepreg in the AFP process". The amount of thread guide resin adhesion was "A", the evaluation of untack occurrence during lamination was "S", and the overall judgment result for passability in the AFP process and laminationability was "A".

[0053] (Comparative Example 1) A slit tape prepreg was prepared by removing particles from the above-mentioned "(1) Slit Tape Prepreg Material," and a processed slit tape prepreg was manufactured according to "(2) Method for Manufacturing Slit Tape Prepreg." Subsequently, the manufactured slit tape prepreg was evaluated according to "(3) Method for Measuring the Thickness of the Coating Layer and Surface Resin Coverage Rate of Slit Tape and (4) Method for Measuring the Surface Roughness of Slit Tape." The results showed an average thickness of 3.2 μm for the surface resin epoxy resin composition layer, a surface roughness Ra of 2.1 μm, and a surface resin coverage rate of 89%. Furthermore, using the manufactured slit tape prepreg, the AFP processability was evaluated according to "(5) Evaluation of AFP Process Passability of Slit Tape Prepreg." The results showed a thread guide resin adhesion amount of "C," an untack occurrence evaluation during lamination of "S," and an overall judgment result of "C" for AFP process passability and laminationability.

[0054] (Comparative Example 2) A processed slit tape prepreg was prepared according to the above-mentioned "(1) Slit tape prepreg material (2) Method for preparing slit tape prepreg". Subsequently, the prepared slit tape prepreg was evaluated according to the above-mentioned "(3) Method for measuring the thickness of the coating layer and the surface resin coverage rate of the slit tape (4) Method for measuring the surface roughness of the slit tape". The average thickness of the surface resin epoxy resin composition layer was 0.9 μm, the surface roughness Ra was 12.5 μm, and the surface resin coverage rate was 72%. Furthermore, using the prepared slit tape prepreg, the AFP processability was evaluated according to the above-mentioned "(5) Evaluation of the passability of the slit tape prepreg in the AFP process". The amount of thread guide resin adhesion was "A", the evaluation of untack occurrence during lamination was "C", and the overall judgment result for passability in the AFP process and laminationability was "C".

[0055] (Comparative Example 3) A processed slit tape prepreg was prepared according to the above-mentioned "(1) Slit tape prepreg material (2) Method for preparing slit tape prepreg". However, in (2), heating of the slit tape prepreg was not performed. Subsequently, the prepared slit tape prepreg was evaluated according to the above-mentioned "(3) Method for measuring the thickness of the coating layer and the surface resin coverage rate of the slit tape (4) Method for measuring the surface roughness of the slit tape". The average thickness of the surface resin epoxy resin composition layer was 15.2 μm, the surface roughness Ra was 2.8 μm, and the surface resin coverage rate was 88%. Furthermore, using the prepared slit tape prepreg, the AFP processability was evaluated according to the above-mentioned "(5) Evaluation of the passability of the slit tape prepreg in the AFP process". The amount of thread guide resin adhesion was "C", the evaluation of untack occurrence during lamination was "A", and the overall judgment result for passability in the AFP process and laminationability was "C".

[0056] (Comparative Example 4) A processed slit tape prepreg was prepared according to the above-mentioned "(1) Slit tape prepreg material (2) Method for preparing slit tape prepreg". Subsequently, the prepared slit tape prepreg was evaluated according to the above-mentioned "(3) Method for measuring the thickness of the coating layer and the surface resin coverage rate of the slit tape (4) Method for measuring the surface roughness of the slit tape". The average thickness of the surface resin epoxy resin composition layer was 9.1 μm, the surface roughness Ra was 1.8 μm, and the surface resin coverage rate was 89%. Furthermore, using the prepared slit tape prepreg, the AFP processability was evaluated according to the above-mentioned "(5) Evaluation of the passability of the slit tape prepreg in the AFP process". The amount of thread guide resin adhesion was "B", the evaluation of untack occurrence during lamination was "S", and the overall judgment result for passability in the AFP process and laminationability was "B".

[0057] (Comparative Example 5) A processed slit tape prepreg was prepared according to the above-mentioned "(1) Slit tape prepreg material (2) Method for preparing slit tape prepreg". Subsequently, the prepared slit tape prepreg was evaluated according to the above-mentioned "(3) Method for measuring the thickness of the coating layer and the surface resin coverage rate of the slit tape (4) Method for measuring the surface roughness of the slit tape". The average thickness of the surface resin epoxy resin composition layer was 5.1 μm, the surface roughness Ra was 11.0 μm, and the surface resin coverage rate was 78%. Furthermore, using the prepared slit tape prepreg, the AFP processability was evaluated according to the above-mentioned "(5) Evaluation of the passability of the slit tape prepreg in the AFP process". The amount of thread guide resin adhesion was "A", the evaluation of untack occurrence during lamination was "B", and the overall judgment result for passability in the AFP process and laminationability was "B".

[0058] [Table 1] [Industrial applicability]

[0059] The slit tape prepreg according to the present invention can be applied to AFP lamination processes used in the aerospace and automotive industries. [Explanation of symbols]

[0060] 1. Surface of slit tape prepreg (cross-sectional view) 11 Carbon fiber layer 12 Covering layer 13. The outermost surface of the carbon fiber layer (interface with the coating layer) 14 Exposed portion of the carbon fiber layer 15 particles 16 Surface of the coating layer 17. Thickness of the coating layer 18. Average surface height of the coating layer 19. Average height of the interface between the carbon fiber layer and the coating layer. 2. Slit tape prepreg processing device 21 Original slit tape prepreg 22 Release film 23 Release film recovery creel 24 Directional Roll 25 Heating section 26 Processed slit tape prepreg 27 Release film supply creel 3. Schematic diagram of the AFP stacking simplified evaluation device. 31 Laminated base material 32 Laminated slit tape prepreg 33 Directional Roll 34 Nip Roll 35 IR heater 36. Thermography of the layered section 37 Creel 38. Measuring sensor 39 Constant temperature and humidity chamber 40 Directional Roll 41 Cut section

Claims

1. A slit tape prepreg obtained by impregnating carbon fibers with an epoxy resin composition, wherein at least one of the slit tape prepreg surfaces has a coating layer satisfying the following conditions [a] to [c]. [a] The coating layer comprises a liquid resin and particles insoluble in the liquid resin. [b] Average thickness of the coating layer is 1 μm or more and 14 μm or less [c] The average surface roughness (arithmetic mean height Ra) of the coating layer is 2 μm or more and 10 μm or less.

2. The slit tape prepreg according to claim 1, characterized in that the surface coverage of the coating layer is 65% or more and 95% or less of the surface of the slit tape prepreg.

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