Thermoplastic prepreg, fiber reinforced plastic and method for manufacturing the same

Abstract

To provide a fiber-reinforced plastic that maintains lightweight and mechanical properties and can cope with a more complex shape. A thermoplastic prepreg in which a thermoplastic resin is impregnated in a network of discontinuous reinforcing fibers, the thermoplastic prepreg satisfying at least one of the following characteristics (A) or (B). Characteristic (A): having a plurality of notches that cut at least a part of the discontinuous reinforcing fibers that constitute the network of discontinuous reinforcing fibers. Characteristic (B): having a fiber length variation region in which the coefficient of variation of the fiber length of the discontinuous reinforcing fibers that constitute the network of discontinuous reinforcing fibers is 40% or more.

Description

TECHNICAL FIELD

[0001] The present application relates to a thermoplastic prepreg comprising a reinforcing fiber and a thermoplastic matrix resin and a manufacturing method thereof, and a fiber-reinforced plastic molded from the prepreg base material and a manufacturing method thereof. BACKGROUND

[0002] Fiber-reinforced plastics formed from a reinforcing fiber and a matrix resin are excellent in specific strength and specific stiffness, and are widely used for electrical and electronic applications, civil engineering and construction applications, automotive applications, sports applications, aircraft applications, and the like. In recent years, in particular, the market demand for fiber-reinforced plastics for industrial products such as automobiles, aircraft, and sports goods has been increasing year by year in terms of the followability of the molding material to complex shapes during molding and the lightweightness of the molded product. In order to meet such demands, compression-molded products of fiber-reinforced plastics having complex shapes and excellent mechanical properties and lightweightness are widely used for various industrial applications.

[0003] Specifically, Patent Literature 1 discloses a slit prepreg in which a unidirectional prepreg in which a continuous reinforcing fiber is impregnated with a resin is provided with a slit that cuts the reinforcing fiber in one direction, thereby improving the shape followability during molding.

[0004] In addition, Patent Literature 2 discloses a prepreg in which the reinforcing fiber is made discontinuous and the molding material is made to be dispersed in multiple directions, thereby achieving a balance between the followability to complex shapes during molding and the mechanical properties of the molded product.

[0005] Further, Patent Literature 3 discloses a technology in which the ratio of the amount of deformation in the in-plane direction generated when a molding base material is pressurized to the amount of deformation in the out-of-plane direction when the pressure is released after pressurization is specified, and the mechanical properties of the molded product and the followability to complex shapes during molding are simultaneously achieved.

[0006] As one method for achieving the lightweightness of the molded product, Patent Literature 4 discloses the use of a core material having a low specific gravity.

[0007] However, a core material having a low specific gravity has a tendency to have poor mechanical properties as a single material. Therefore, in the case of using such a core material, in order to ensure the mechanical properties of the molded product, Patent Literature 5 discloses a product design in which a high-rigidity skin material or the like is arranged on the outer periphery of the core material. However, in a product designed in this way, the mass is necessarily increased, or the thickness has to be increased. That is, even if the lightweightness of the product can be achieved as a result, the degree thereof is relatively small. In addition, the skin material used in order to ensure the mechanical properties of the molded product is generally poor in shape followability to complex shapes, and thus the shape that can be molded is limited.

[0008] PRIOR ART DOCUMENTS

[0009] PATENT LITERATURE

[0010] Patent Literature 1: Japanese Patent Application Laid-Open No. 2008-207544

[0011] Patent Literature 2: Japanese Patent Application Laid-Open No. 2010-235779

[0012] Patent Literature 3: International Publication No. 2019 / 189384

[0013] Patent Literature 4: International Publication No. 2017 / 110528

[0014] Patent Literature 5: International Publication No. 2015 / 029634 SUMMARY

[0015] PROBLEMS TO BE SOLVED BY THE INVENTION

[0016] The fiber-reinforced plastic for industrial products is required to have a convex-concave portion such as a rib shape, a deep-drawing portion, a wall thickness varying portion, and the like in order to improve mechanical properties and functionality, and the molding material is required to have followability to a complex shape, but in the invention described in Patent Literature 1, since the orientation direction of the fiber is unidirectional, the shape followability is anisotropic, and the shape that can be molded is limited. In addition, since the mechanical properties of the resulting reinforced fiber plastic are also anisotropic, the orientation direction of the fiber needs to be designed and layered.

[0017] In the invention described in Patent Literature 2, since the reinforcing fiber is discontinuous, although it has a certain shape followability, in the case where the discontinuous fiber is oriented in multiple directions, since the fibers having different orientation directions interfere with each other, it is insufficient for molding with large deformation.

[0018] In addition, in the invention described in Patent Literature 3, although the molding of a complex shape is easy by in-plane deformation and out-of-plane deformation, the shape that can be molded is limited, and it is difficult to mold into a desired shape.

[0019] Further, in the manufacturing method of the structure described in Patent Literature 4 and Patent Literature 5, the shape followability at the time of molding is limited, and sometimes it is difficult to mold into a complex shape.

[0020] From the above, there is a demand for a fiber-reinforced plastic material having high mechanical properties and followability to a complex shape, and light weight. The present invention was made in view of the above problems, and aims to provide a fiber-reinforced plastic material capable of simultaneously achieving high mechanical properties of a molded product, followability to a complex shape at the time of molding, and light weight of the molded product.

[0021] MEANS FOR SOLVING THE PROBLEMS

[0022] One aspect of the present invention for solving the above-mentioned problems is a thermoplastic prepreg preform, which is formed by impregnating a discontinuous reinforcing fiber web with thermoplastic resin, wherein the aforementioned thermoplastic prepreg preform satisfies at least one of the following characteristics (A) or (B).

[0023] Feature (A): having a plurality of cuts that cut at least a portion of the discontinuous reinforcing fibers constituting the aforementioned discontinuous reinforcing fiber web;

[0024] Feature (B): A region of fiber length variation in which the coefficient of variation of the fiber length of the discontinuous reinforcing fibers constituting the aforementioned discontinuous reinforcing fiber web is 40% or more.

[0025] Furthermore, another aspect of the present invention typically known as a fiber-reinforced plastic obtained by molding this thermoplastic prepreg preform is a fiber-reinforced plastic having a thermoplastic resin layer comprising discontinuous reinforcing fibers and thermoplastic resin, wherein the aforementioned fiber-reinforced plastic satisfies at least one of the following characteristics (C) or (D).

[0026] Feature (C): The aforementioned thermoplastic resin layer contains an end-arrangement structure in which the ends of the aforementioned discontinuous reinforcing fibers oriented in three or more directions are continuously arranged;

[0027] Feature (D): The fiber length variation portion having a coefficient of variation of 40% or more for the fiber length of the discontinuous reinforcing fibers contained in the aforementioned thermoplastic resin layer.

[0028] Furthermore, the method for manufacturing the thermoplastic prepreg preform as described above, and the method for manufacturing fiber-reinforced plastics using the thermoplastic prepreg preform of the present invention are also described as embodiments of the present invention.

[0029] The effects of the invention

[0030] According to the present invention, thermoplastic prepreg blanks with high conformability to complex shapes and high mechanical properties can be obtained, thereby enabling the production of fiber-reinforced plastics with good surface quality, high mechanical properties, and lightweight, even with complex shapes. Attached Figure Description

[0031] Figure 1 This is a schematic diagram illustrating an example of the thermoplastic prepreg blank of the present invention.

[0032] Figure 2 This is a schematic diagram showing an example of a cross-section in the thickness direction of the thermoplastic prepreg blank of the present invention.

[0033] Figure 3 This is a schematic diagram illustrating an example of the configuration of the cuts in the thermoplastic prepreg blank of the present invention.

[0034] Figure 4is an example of a histogram showing a typical fiber length distribution in a fiber length variation region of a thermoplastic prepreg of the present application, or in a fiber length variation portion of a fiber reinforced plastic.

[0035] Figure 5 is a schematic view showing an example of an orientation state of reinforcing fibers of a thermoplastic prepreg of the present application.

[0036] Figure 6 is a schematic view showing an example of an end portion arrangement structure of a continuous arrangement of a fiber reinforced plastic of the present application.

[0037] Figure 7 is a schematic view showing an example of an embodiment of the present application.

[0038] Figure 8 is a schematic view for supplementing the explanation on the moldability test. DETAILED DESCRIPTION

[0039] <Thermoplastic prepreg>

[0040] The thermoplastic prepreg of the present application (hereinafter sometimes simply referred to as "prepreg") is one in which a thermoplastic resin is impregnated in a network of discontinuous reinforcing fibers, and the aforementioned thermoplastic prepreg satisfies at least one of the following characteristics (A) or (B),

[0041] Characteristic (A): has a plurality of cutouts that cut at least a portion of the discontinuous reinforcing fibers that constitute the network of discontinuous reinforcing fibers;

[0042] Characteristic (B): has a fiber length variation region in which the coefficient of variation of the fiber length of the discontinuous reinforcing fibers that constitute the network of discontinuous reinforcing fibers is 40% or more.

[0043] The network of discontinuous reinforcing fibers is an aggregate of discontinuous reinforcing fibers, and has at least a portion in which the discontinuous reinforcing fibers that constitute the aggregate are in direct contact with each other, or a portion in which the discontinuous reinforcing fibers that constitute the aggregate are bonded to each other via an adhesive resin described later.

[0044] The reinforcing fiber used as a discontinuous reinforcing fiber (hereinafter sometimes referred to simply as "reinforcing fiber") is not particularly limited, and for example, carbon fiber, glass fiber, aramid fiber, alumina fiber, silicon carbide fiber, boron fiber, metal fiber, natural fiber, mineral fiber, or the like can be used, and two or more kinds thereof can also be used in combination. Among them, from the viewpoint of high specific strength, high specific rigidity, and excellent lightweight effect, it is preferable to use carbon fiber of a PAN-based, pitch-based, or rayon-based type. In addition, from the viewpoint of improving the economy of the obtained molded article, it is preferable to use glass fiber. From the viewpoint of balance between mechanical properties and economy, it is also preferable to use a combination of carbon fiber and glass fiber. Furthermore, from the viewpoint of improving the impact absorption and the shapeability of the obtained molded article, it is preferable to use aramid fiber. From the viewpoint of balance between mechanical properties and impact absorption, it is also preferable to use a combination of carbon fiber and aramid fiber. Alternatively, from the viewpoint of improving the electrical conductivity of the obtained molded article, it is also possible to use a reinforcing fiber coated with a metal such as nickel, copper, or ytterbium.

[0045] The reinforcing fiber contained in the thermoplastic prepreg of the present application is a discontinuous reinforcing fiber. By making the reinforcing fiber contained in the prepreg discontinuous, a fiber-reinforced plastic having an excellent shape followability and a complex shape can be easily manufactured. In the present specification, the discontinuous reinforcing fiber refers to a reinforcing fiber having an average fiber length of 100 mm or less. The average fiber length of the discontinuous reinforcing fiber is preferably in the range of 2 mm or more and 20 mm or less. By setting it to this range, the balance between mechanical properties and shape followability can be excellent.

[0046] As a method for measuring the fiber length of the reinforcing fiber, for example, there are a method of directly picking up the reinforcing fiber from the discontinuous reinforcing fiber web to measure it, and a method (dissolution method) of dissolving using a solvent that dissolves only the thermoplastic resin in the prepreg or in the molded fiber-reinforced plastic, filtering out the remaining reinforcing fiber, and measuring it by microscope observation. In addition, in the absence of a solvent that dissolves the thermoplastic resin, there is a method (burn-off method) of burning off only the thermoplastic resin in a temperature range in which the reinforcing fiber does not undergo oxidative degradation, separating the reinforcing fiber, and measuring it by microscope observation. By such a method, 100 discontinuous reinforcing fibers are randomly taken out from the prepreg or the molded fiber-reinforced plastic, the length of each is measured to the nearest 1 μm unit using an optical microscope, and the average value is taken as the average fiber length. Note that, in the case of comparing the method of directly picking up the reinforcing fiber from the discontinuous reinforcing fiber web with the method of picking up the reinforcing fiber in the burn-off method or the dissolution method, by appropriately selecting the conditions, the results obtained do not differ significantly, but in the present application, in the case where the average fiber length calculated from the fiber length measured by either method and the coefficient of variation thereof fall within the aforementioned numerical range, it is assumed that the aforementioned conditions are satisfied. Note that, in selecting the conditions, in the dissolution method, by selecting the solvent on the basis of whether or not the solvent used can dissolve the thermoplastic resin, or the time required for dissolution, the amount of solvent required, appropriate conditions can be selected, and in the burn-off method, appropriate conditions can be set on the basis of the thermal decomposition temperature of the thermoplastic resin, the time required, and the like.

[0047] As the discontinuous reinforcing fiber web, a nonwoven fabric obtained by a dry method or a wet method is preferable. The nonwoven fabric obtained by the dry method or the wet method easily disperses the discontinuous reinforcing fiber randomly, and as a result, a prepreg having isotropic mechanical properties and moldability can be obtained.

[0048] As the discontinuous reinforcing fiber web, the reinforcing fibers can also be filled with other components such as an adhesive resin. As the adhesive resin, from the viewpoint of the adhesion of the resin to the reinforcing fiber, and the viewpoint of ensuring the operability of only the reinforcing fiber, any one selected from a thermoplastic resin and a thermosetting resin is preferable. From the viewpoint of the adhesion of the resin to the reinforcing fiber, a resin of the same kind as or having compatibility with the thermoplastic resin to be impregnated later is selected, and from the viewpoint of ensuring the operability of the reinforcing fiber, a water solution, a dispersion, an emulsion of a thermosetting resin and a thermoplastic resin is preferable.

[0049] The discontinuous reinforcing fibers contained in such a discontinuous reinforcing fiber web are generally oriented in more than three directions in the plane. In this way, an isotropy having a shape followability at the time of molding and high mechanical properties at the time of producing a fiber reinforced plastic is obtained. In addition, in the case of a prepreg in which the reinforcing fibers are unidirectionally laid (hereinafter referred to as a unidirectional prepreg), in order to exhibit a desired shape followability and mechanical properties, a process of stacking a plurality of unidirectional prepregs is required, and in order to obtain a quasi-isotropy, the number of stacked sheets (i.e., the thickness of the molded product) is sometimes limited. In contrast, in the thermoplastic prepreg of the present application in which the reinforcing fibers are oriented in more than three directions in the plane, an isotropy can be obtained in an arbitrary number of stacked sheets while saving the time for stacking the prepregs.

[0050] A method for confirming that the reinforcing fibers are oriented in more than three directions in the plane will be described below. One of the discontinuous reinforcing fibers contained in a prepreg is selected, and the orientation direction (the direction of a straight line connecting both ends of the discontinuous reinforcing fiber) of the discontinuous reinforcing fiber in the plane of the prepreg is defined as the direction of 0°. Here, the "plane of the prepreg" means that the judgment is made in the plane projected onto a plane parallel to the prepreg. At this time, in the case where other discontinuous reinforcing fibers intersecting the discontinuous reinforcing fiber at an angle of more than 10° in the plane exist on both the clockwise side and the counterclockwise side from 0°, it is considered in the present application that the reinforcing fibers are oriented in more than three directions in the plane. Note that the "intersection" here means that it is not necessary to overlap the two discontinuous reinforcing fibers as the object in the thickness direction, and also includes the case where the extended lines of the respective discontinuous reinforcing fibers are intersected.

[0051] As a method for measuring the orientation state of the reinforcing fibers, for example, a method for observing the orientation of the reinforcing fibers from the surface of the prepreg can be exemplified. In this case, the fibers are exposed by polishing the surface of the prepreg, and thus the reinforcing fibers are more easily observed. In addition, a method for observing the orientation of the reinforcing fibers by using transmitted light with respect to the prepreg can be exemplified. In this case, the prepreg is cut into a thin sheet, and thus the reinforcing fibers are more easily observed. Furthermore, a method for observing the orientation of the reinforcing fibers by using X-ray CT to take an image of the prepreg can be exemplified. In the case of a reinforcing fiber having a high X-ray transmissivity, the reinforcing fiber is more easily observed if a fiber for tracing is mixed in the reinforcing fiber, or a medicine for tracing is applied to the reinforcing fiber.

[0052] The thermoplastic resin impregnated in the discontinuous reinforcing fiber web used in the prepreg of the present application is not particularly limited, and for example, crystalline resins such as "polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), liquid crystal polyester, and the like, polyethylene (PE), polypropylene (PP), polybutylene, and the like, polyoxymethylene (POM), polyamide (PA), polyphenylene sulfide (PPS), and the like, polyketone (PK), polyether ketone (PEK), polyether ether ketone (PEEK), polyether ketone ketone (PEKK), polyether nitrile (PEN), polytetrafluoroethylene, and the like, liquid crystal polymer (LCP)", and the like, non-crystalline resins such as "polycarbonate (PC), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyphenylene ether (PPE), polyimide (PI), polyamide-imide (PAI), polyetherimide (PEI), polysulfone (PSU), polyether sulfone, polyarylate (PAR)", and the like, except for styrene-based resins, phenol-based resins, phenoxy-based resins, and thermoplastic elastomers such as polystyrene-based, polyolefin-based, polyurethane-based, polyester-based, polyamide-based, polybutadiene-based, polyisoprene-based, fluorine-based resins, and acrylonitrile-based, and the like, copolymers and modified products thereof, and the like, can be mentioned. Among these, from the viewpoint of light weight of the resulting molded article, polyolefins are preferred, from the viewpoint of strength, polyamides are preferred, from the viewpoint of surface quality, non-crystalline resins such as polycarbonates, styrene-based resins are preferred, from the viewpoint of heat resistance, polyarylene sulfides are preferred, from the viewpoint of continuous use temperature, polyether ether ketones are preferred, and from the viewpoint of chemical resistance, fluorine-based resins are preferred.

[0053] A blend resin containing a plurality of the above-described thermoplastic resins can also be used as the thermoplastic resin, and as long as the main component of the thermoplastic resin matrix (a component greater than 50% by weight when the entire matrix is taken as 100% by weight) is a thermoplastic resin, a blend resin mixed with a thermosetting resin can also be used.

[0054] The thermoplastic prepreg of the present application preferably contains 40% by weight or more and 90% by weight or less of the aforementioned thermoplastic resin, and 10% by weight or more and 60% by weight or less of the aforementioned discontinuous reinforcing fiber. By being this way, the balance between the shape followability and the mechanical properties is excellent, and thus is preferred. The weight ratio of the aforementioned thermoplastic resin and the aforementioned discontinuous reinforcing fiber is not particularly limited as long as it is within the aforementioned range, and, in the case where the balance between the shape followability and the mechanical properties is valued, it is preferred to contain 50% by weight or more and 80% by weight or less of the aforementioned thermoplastic resin, and 20% by weight or more and 50% by weight or less of the aforementioned discontinuous reinforcing fiber; in the case where the shape followability is valued, it is preferred to contain 60% by weight or more and 90% by weight or less of the aforementioned thermoplastic resin, and 10% by weight or more and 40% by weight or less of the aforementioned discontinuous reinforcing fiber; and in the case where the mechanical properties are valued, it is preferred to contain 40% by weight or more and 70% by weight or less of the aforementioned thermoplastic resin, and 30% by weight or more and 60% by weight or less of the aforementioned discontinuous reinforcing fiber.

[0055] As the first way for the thermoplastic prepreg of the present application, there is a way satisfying the characteristic (A) having a plurality of incisions cutting at least a part of the discontinuous reinforcing fibers constituting the discontinuous reinforcing fiber web. By the incisions, the fiber length of a part of the reinforcing fibers is further shortened, and the end portions of the cut reinforcing fibers are arranged in a straight line or a curved line, and thus, in the molding of a complex shape, the incisions are not opened because the reinforcing fibers are not tight. Further, by cutting the reinforcing fibers with the incisions, the transmission of the interference of the reinforcing fibers with each other is interrupted, and the complex shape is easily followed.

[0056] Hereinafter, the present application will be described with appropriate reference to the accompanying drawings for easy understanding, but the present application is not limited by any of these drawings. Further, the description of the specific embodiments shown in the drawings can be understood as the description of the upper concept of the thermoplastic prepreg of the present application.

[0057] Figure 1 In the illustrated embodiment, the thermoplastic prepreg 3 has incisions 1 cutting at least a part of the discontinuous reinforcing fibers. The incisions can be provided over the entire surface of the thermoplastic prepreg, or can be provided only in a part. Further, in the case where the incisions do not penetrate in the thickness direction of the discontinuous reinforcing fiber web, they can be provided on both surfaces, or can be provided on only either surface. In this specification, the region where the incisions are provided on the surface of the thermoplastic prepreg is referred to as an "incision region". As Figure 1As shown, the boundary of the cutout region 2 is divided by a line segment group that is formed by connecting line segments connecting the end portions of the outermost cutouts present in the region. Such a line segment group is drawn in a manner that includes all the cutouts in the line segment group and the total length of the line segment group becomes the smallest. That is, the thermoplastic prepreg of the present application can be one in which the entire surface is a cutout region, or one in which a cutout region is provided on a part of the surface. Note that, Figure 1 In the present embodiment, there is only one cutout region in the range shown in (a), but there can be a plurality of cutout regions. In the case where cutout regions are adjacent, in determining whether it is a plurality of cutout regions or one large cutout region, first, in the case where it is assumed that there are two adjacent cutout regions, the average distance of the cutouts in each of the adjacent cutout regions is calculated, and if either of the average distances is shorter than the endmost distance between the two regions assumed to be adjacent, it is set as the case where the assumption is correct, and it is set as two regions.

[0058] The shape of the cutout is not particularly limited, and can be a straight line shape, can be a shape having a broken line portion, or can be a shape having a curved portion in part or all, but in order to stably provide the cutout, it is preferable that the cutout be a straight line shape.

[0059] The length of the cutout is not particularly limited, and in order to easily open the cutout at the time of molding, it is preferable that it be 0.1 mm or more, and more preferably 0.5 mm or more. On the other hand, in order to have sufficient mechanical properties when the thermoplastic prepreg of the present application is molded to produce a fiber-reinforced plastic, the length of the cutout is preferably 50 mm or less, and more preferably 10 mm or less. Note that the length of the cutout refers to the length along the cutout from the end portion of one side of the cutout to the end portion of the other side. Note that in the case where the length of the cutout varies in the thickness direction of the prepreg, the length along the cutout from the end portion of one side of the cutout to the end portion of the other side on the surface of the prepreg is taken as the length of the cutout.

[0060] The cutout is preferably one that reaches a depth of 50% or more to 100% or less of the thickness direction of the aforementioned discontinuous reinforcing fiber web. By being in this form, the cutout easily opens at the time of molding, and high shape followability is exhibited. The depth of the cutout can be the same in all the cutouts, or can be different for each cutout, but from the viewpoint of easily controlling the shape followability, it is more preferable that all the cutouts have the same cutout depth. Here, the depth of the cutout is defined as the depth of the cutout from the surface of the prepreg to the end portion of the cutout on the opposite side. Figure 2 The depth reached by the cutout is described. Figure 2is a schematic view of a cross section parallel to the thickness direction of a cutout including a thermoplastic prepreg. The depth of the cutout refers to the distance 8 in the thickness direction from the surface 5 on the side where the cutout 1 is inserted to the front end 7 of the cutout in the discontinuous reinforcing fiber web 4. In this specification, the cross section of the prepreg is observed in the thickness direction and the cross section where 10 or more cutouts are exposed, 10 cutouts are arbitrarily extracted from the cutouts included in the cross section, the depth of the aforementioned cutouts is measured, and the average of the depths of the 10 extracted cutouts is taken as the cutout depth. In addition, the thickness of the discontinuous reinforcing fiber web refers to the distance 9 between the two surfaces of the discontinuous reinforcing fiber web measured at 10 positions near the cutout where the depth of the cutout of the cross section is measured, and the average of the distances between the surfaces measured at the 10 positions is taken as the thickness of the discontinuous reinforcing fiber web. The depth 8 of the cutout and the thickness 9 of the discontinuous reinforcing fiber web are the same value in the case where the cutout 1 penetrates the discontinuous reinforcing fiber web 4. The ratio of the cutout depth is calculated by (average of the depths of the cutouts) ÷ (average of the thicknesses of the discontinuous reinforcing fiber webs) x 100 (%).

[0061] In the cutout region, it is preferable that the cutouts be regularly arranged. By doing so, uniform shape followability can be exhibited, and large-scale damage caused by the cutouts connecting to each other at the time of molding can be suppressed. Note that if a thermoplastic prepreg having a cutout region where the cutouts are not regularly arranged is used, the shape followability of the prepreg can be reduced, and the prepreg can be damaged at the time of molding. Figure 3 By way of explanation, the aforementioned cutouts being regularly arranged means that 90% or more of the area of the aforementioned cutout region 2 of the thermoplastic prepreg is a case where cutout units 10 including two or more cutouts 1 are arranged.

[0062] It is preferable that, in the cutout region, the intervals between adjacent cutouts be constant and the lengths of all the cutouts be constant. Adjacent cutouts refer to cutouts other than an arbitrary one cutout with respect to the one cutout, and the cutouts whose intervals from each other are the shortest. The intervals between the cutouts refer to the distances between the points (midpoints of the cutouts) that bisect the lengths of the cutouts along the cutouts. By the intervals between adjacent cutouts being constant and the lengths of all the cutouts being constant for the cutouts included in one cutout region, a thermoplastic prepreg having uniform properties in the cutout region is obtained, and thus this is preferable.

[0063] The sum of the cutout lengths per 1 m 2 in the cutout region is preferably 40 m or more. By doing so, the shape followability of the prepreg is greatly improved. More preferably, the sum of the cutout lengths per 1 m 2 is 100 m or more, and more preferably 200 m or more. The upper limit of the sum of the cutout lengths is not particularly limited, but in order for the prepreg not to be greatly broken at the time of molding, it is preferable that the sum be 1000 m or less. In the case where the sum of the cutout lengths is converted, the distances between the surfaces of the aforementioned cutout region 2 at 10 positions where the area is at least 0.01 m2 The sum of the cut lengths of the surface and the back of the above prepreg is converted to the sum of the cut lengths per 1 m 2 of the prepreg. In the case where the sum of the cut lengths of the surface and the back is different, the larger value is used as the sum of the cut lengths. For example, in the case where the area of the cutout region 2 of each of the surface and the back is 0.01 m 2 of the prepreg is 0.5 m and the sum of the cut lengths of the other surface is 1 m, the sum of the cut lengths converted to per 1 m 2 is 100 m.

[0064] The sum of the cut lengths converted to per 1 m 2 in the cutout region is more preferably 40 m or more and 500 m or less. In this way, the shape followability in the out-of-plane direction of the prepreg can be made high, and the shape followability in the in-plane direction can also be maintained high, and the balance of the shape followability in each direction is excellent.

[0065] For the thermoplastic prepreg of the present application, as the second mode, a mode satisfying the characteristic (B) having a fiber length variation region in which the coefficient of variation of the fiber length of the discontinuous reinforcing fiber constituting the above discontinuous reinforcing fiber web is 40% or more can be cited. The coefficient of variation is a value calculated from the standard deviation ÷ average value x 100. In the fiber length variation region, there are discontinuous reinforcing fibers in which the fiber length distribution is wide, and as a result, the shape followability of the fiber length variation region of the prepreg can be made excellent.

[0066] The coefficient of variation of the fiber length in the fiber length variation region is preferably 50% or more and more preferably 60% or more. In order to better express the balance of the shape followability and the mechanical properties, the coefficient of variation is preferably 200% or less. On the other hand, if the coefficient of variation of the fiber length is less than 40%, it is sometimes difficult to simultaneously achieve the mechanical properties and the shape followability. The thermoplastic prepreg of the present application can obtain a fiber reinforced plastic having a complex shape and excellent mechanical properties and lightweight by having high shape followability due to the fiber length variation region.

[0067] In the present application, it is only necessary that a fiber length variation region be present in at least a portion of the prepreg. Specifically, in the case where the prepreg is divided into a grid of square elements each having a side of 50 mm x 50 mm in plan view, it is only necessary that the coefficient of variation of fiber length be 40% or greater in one or more elements. In addition, in the present application, in the case of such division, the collection of elements having a coefficient of variation of fiber length of 40% or greater is regarded as a "fiber length variation region". The proportion of the fiber length variation region in the prepreg is not particularly limited and should be appropriately designed in accordance with the shape of the molded article or the like. In the present application, it is also possible that the entire prepreg be formed of a fiber length variation region. Note that in the case where the prepreg that is the object does not satisfy the grid size, the entire prepreg is regarded as one of the aforementioned elements.

[0068] The prepreg of the present application is preferably produced such that, in the aforementioned fiber length variation region, when a histogram showing the fiber length distribution of the aforementioned discontinuous reinforcing fibers is produced under the following conditions, the highest frequency is 70% or less,

[0069] Conditions: The lengths of discontinuous reinforcing fibers randomly selected from the discontinuous reinforcing fibers contained in the fiber length variation region are measured, and a histogram having a group number of 9 is produced by dividing the range from the smallest fiber length to the largest fiber length into 9 equal parts. When the number of the aforementioned randomly selected discontinuous reinforcing fibers is taken as 100%, the frequency is set as the proportion [%] of the number of discontinuous reinforcing fibers belonging to each group.

[0070] Here, the use of Figure 4 The above conditions are described in detail. Figure 4 is a graph schematically showing a typical fiber length distribution histogram of the discontinuous reinforcing fibers contained in the fiber length variation region. Figure 4In the graph, the vertical axis is the frequency, and the horizontal axis is the fiber length of the discontinuous reinforcing fiber. The fiber length of 100 reinforcing fibers randomly measured according to the measurement method of the average fiber length of the reinforcing fiber described above is made into a histogram with 9 groups. The group means that the number of groups is set to 9 by equally dividing the range from the smallest fiber length to the largest fiber length in the 100 measured into 9. In addition, from the group with the shortest fiber length, it is sequentially called the first group, the second group, the third group,..., the ninth group. For example, in the case where the smallest fiber length is 1.0 mm and the largest fiber length is 19.0 mm in the 100 measured fiber lengths, the first group is 1.0 mm or more and less than 3.0 mm; the second group is 3.0 mm or more and less than 5.0 mm; the third group is 5.0 mm or more and less than 7.0 mm; the fourth group is 7.0 mm or more and less than 9.0 mm; the fifth group is 9.0 mm or more and less than 11.0 mm; the sixth group is 11.0 mm or more and less than 13.0 mm; the seventh group is 13.0 mm or more and less than 15.0 mm; the eighth group is 15.0 mm or more and less than 17.0 mm; and the ninth group is 17.0 mm or more and less than 19.0 mm. In the histogram, when the number of the aforementioned randomly selected discontinuous reinforcing fibers is 100%, the frequency is set as the proportion [%] of the number of the discontinuous reinforcing fibers belonging to each group.

[0071] In the aforementioned histogram, the group 12 with a longer fiber length than the group 11 with the highest frequency is formed of the discontinuous reinforcing fibers having a relatively long fiber length among the discontinuous reinforcing fibers contained in the prepreg of the present application, and therefore they are collectively called a long fiber group 13. On the other hand, the group 11 with the highest frequency and the group 14 with a shorter fiber length than this group are formed of the discontinuous reinforcing fibers having a relatively short fiber length, and therefore they are collectively called a short fiber group 15. The discontinuous reinforcing fibers belonging to the aforementioned long fiber group 13 have the effect of being lightweight and exhibiting high mechanical properties when a fiber-reinforced plastic is made using the prepreg of the present application. On the other hand, the discontinuous reinforcing fibers belonging to the short fiber group 15 are capable of exhibiting high followability to a complex shape and high dimensional accuracy when a fiber-reinforced plastic is made using the prepreg of the present application. Note that when the group with the highest frequency is determined, in the case where there are a plurality of groups with the same frequency, the group with the longest fiber length among these groups is adopted.

[0072] In the fiber length variation region, the highest frequency in the aforementioned histogram is preferably 70% or less. Thereby, a fiber-reinforced plastic in which the balance of the fiber length of the discontinuous reinforcing fiber is excellent and in which the mechanical properties and the shape followability are both achieved can be obtained. The more preferable range of the highest frequency in the aforementioned histogram is 60% or less, and more preferably 50% or less.

[0073] Further, in the fiber length variation region, it is more preferable that there are three or more groups in the aforementioned histogram in which the frequency is 10% or more. This means that the width of the fiber length distribution of the discontinuous reinforcing fibers is wide, and as a result, it is easier to achieve both shape followability and mechanical properties. The more preferable number of groups in which the frequency is 10% or more is four or more, and more preferably five or more.

[0074] The thermoplastic prepreg of the present application satisfies at least one of the aforementioned characteristic (A) or the aforementioned characteristic (B). By satisfying both the aforementioned characteristic (A) and the aforementioned characteristic (B), the shape followability in both the in-plane direction and the out-of-plane direction is excellent, and the molded fiber reinforced plastic exhibits excellent mechanical properties, and thus is more preferable.

[0075] By heating the thermoplastic prepreg of the present application to a temperature above the melting or softening temperature of the aforementioned thermoplastic resin, expansion is caused by the fuzzing force of the discontinuous reinforcing fibers. In particular, when the thickness of a precursor obtained by cutting only the aforementioned cutout region or the aforementioned fiber length variation region from the thermoplastic prepreg of the present application is set to R [mm], and the thickness of the fiber reinforced plastic obtained by heating the aforementioned precursor to a temperature above the melting or softening temperature of the aforementioned thermoplastic resin and then keeping the aforementioned precursor for 1 hour under atmospheric pressure is set to S [mm], it is preferable that the expansion ratio calculated from S / R is 2.0 or more from the viewpoint of the followability to a complex shape and the lightweight property of the fiber reinforced plastic to be produced. The more preferable range of the expansion ratio is 3.0 or more, and more preferably 5.0 or more.

[0076] It is more preferable that the thermoplastic prepreg of the present application satisfies the aforementioned characteristic (A) and the aforementioned characteristic (B), and that a plurality of cutouts in which at least a part of the reinforcing fibers included in the discontinuous reinforcing fiber web is cut are formed in the aforementioned fiber length variation region. By the cutouts, the fiber length of a part of the reinforcing fibers is shortened, and it is easy to form the variation state of the fiber length of the discontinuous reinforcing fibers, and the end portions of the cut reinforcing fibers are arranged in a straight line or a curved line, and thus, in the molding of a complex shape, the cutouts are not opened because the reinforcing fibers are not tight. Further, by cutting the reinforcing fibers using the cutouts, the transmission of the interference of the reinforcing fibers with each other is interrupted, and it is easy to follow a complex shape. As the cutouts formed in the fiber length variation region, the same cutouts as the aforementioned cutouts can be used. In this way, the shape followability in both the in-plane direction and the out-of-plane direction is excellent, and the fiber length variation region can be formed in a so-called cutout insertion efficient means, and thus a thermoplastic prepreg excellent in productivity can be obtained.

[0077] In the thermoplastic prepreg of the present application, the discontinuous reinforcing fibers are preferably in a single fiber form. By the reinforcing fibers being in a single fiber form, the prepreg has more homogeneous shape followability, exhibits homogeneous mechanical properties when molded, and is able to suppress concentration of stress to the ends of the reinforcing fibers, exhibiting high mechanical properties. Here, the reinforcing fibers being in a single fiber form means that in the prepreg, the reinforcing fiber filaments are not bundled but are independently dispersed. In the present application, for the reinforcing fiber filaments arbitrarily selected from the prepreg and the reinforcing fiber filaments intersecting the reinforcing fiber filaments, if the proportion of the reinforcing fiber filaments for which the two-dimensional orientation angle described later is 1° or more is 80% or more, it is determined that the discontinuous reinforcing fibers are in a single fiber form. Here, since it is difficult to determine all of the reinforcing fiber filaments intersecting the selected reinforcing fiber filaments, 20 intersecting reinforcing fiber filaments are randomly selected to measure the two-dimensional orientation angle. This measurement is repeated 5 times in total with other reinforcing fiber filaments, and the proportion of the single fibers for which the two-dimensional orientation angle is 1° or more is calculated.

[0078] Using Figure 5 The two-dimensional orientation angle is described in detail. Figure 5 is a schematic view showing the dispersion state of the reinforcing fibers when only the reinforcing fibers are extracted from the thermoplastic prepreg of the present application and observed from the thickness direction. Here, observation from the thickness direction means observation of a projection image onto a plane parallel to the thermoplastic prepreg. If attention is paid to the reinforcing fiber filament 16a, the reinforcing fiber filament 16a intersects the reinforcing fiber filaments 16b to 16f. The intersection here means a state in which the reinforcing fiber filament of interest is observed to intersect the other reinforcing fiber filaments in the two-dimensional plane observed, and in the actual prepreg, the reinforcing fiber filament 16a does not necessarily have to be in contact with the reinforcing fiber filaments 16b to 16f. The two-dimensional orientation angle is defined as the angle 17 of 0° or more and 90° or less of the two angles formed by the two reinforcing fiber filaments intersecting each other.

[0079] Specifically, the method of measuring the average value of the two-dimensional orientation angle from the thermoplastic prepreg is not particularly limited, and for example, the same method as that of observing the orientation of the reinforcing fibers from the surface of the prepreg can be exemplified.

[0080] Also, in the thermoplastic prepreg of the present application, the discontinuous reinforcing fibers are preferably randomly oriented in the plane. By this, homogeneous isotropic shape followability and mechanical properties are exhibited. In the present application, the reinforcing fibers being randomly oriented in the plane means a state in which the average value of the two-dimensional orientation angle of the reinforcing fibers is in the range of 30° or more and 60° or less. The average value of the two-dimensional orientation angle is more preferably in the range of 40° or more and 50° or less, and is more preferably closer to 45°, which is the ideal angle. The average value of the two-dimensional orientation angle of the present application is calculated by adding up the two-dimensional orientation angles of the reinforcing fiber filaments randomly selected from the prepreg (20 filaments) and dividing the sum by the number of the reinforcing fiber filaments (20). Figure 5All reinforcing fiber monofilaments (16a) intersected in the middle ( Figure 5 The average value of the two-dimensional orientation angles of the reinforcing fiber monofilaments 16b to 16f was measured. When there were multiple reinforcing fiber monofilaments crossing reinforcing fiber monofilament 16a, 20 crossing reinforcing fiber monofilaments were randomly selected for measurement. The measurement was repeated 5 times with other reinforcing fiber monofilaments, and the average value of 100 two-dimensional orientation angles was set as the average value of the two-dimensional orientation angles.

[0081] Fiber-reinforced plastics can be obtained by molding the thermoplastic prepreg blanks as described above, either individually or by stacking two or more sheets together. In particular, molding two or more thermoplastic prepreg blanks integrally prevents large-scale breakage caused by deformation of only specific prepreg blanks during molding, which is preferable. Furthermore, it allows for greater freedom in thickness design, expanding the range of shapes that can be molded. In this invention, the method of forming two or more thermoplastic prepreg blanks is not particularly limited; it can be a method where the sides of multiple thermoplastic prepreg blanks are connected to each other and arranged in-plane. However, it is preferred that the two or more thermoplastic prepreg blanks are stacked together, i.e., adjacent thermoplastic prepreg blanks in the thickness direction overlap at least partially when viewed in the thickness direction. Additionally, "integration" refers to a state where each thermoplastic prepreg blank is bonded to adjacent thermoplastic prepreg blanks. As a bonding method, for example, the entire or part of the thermoplastic prepreg laminate can be heated to soften the resin, and then the resin can be cured by cooling to achieve bonding. Alternatively, an adhesive layer can be provided between the prepreg layers, and bonding can be achieved through the components of the adhesive layer.

[0082] In addition, to improve mechanical properties, designability, etc., such fiber-reinforced plastics may also have layers other than the prepreg blank of the present invention.

[0083] <Method for manufacturing thermoplastic prepreg preforms>

[0084] As an example, the thermoplastic prepreg blank of the present invention can be manufactured by a manufacturing method having the following steps: a step of making a discontinuous reinforcing fiber web (web making step); a step of impregnating the discontinuous reinforcing fiber web with thermoplastic resin (impregnation step); and a step of inserting a plurality of cuts in such a way that at least a portion of the discontinuous reinforcing fibers contained in the discontinuous reinforcing fiber web is cut off (cutting step).

[0085] As a web-making process, for example, dry papermaking or wet papermaking is preferred to produce discontinuous reinforcing fiber webs from dispersed discontinuous reinforcing fibers.

[0086] As the impregnation process, for example, the following method can be given: a laminate is made by alternately stacking one or more of the aforementioned discontinuous reinforcing fiber webs and one or more of the thermoplastic resin sheets, the laminate is raised to above the melting point of the thermoplastic resin to soften the thermoplastic resin, and then pressure is applied to impregnate the thermoplastic resin into the voids of the discontinuous reinforcing fiber web, thereby making a one-layer prepreg.

[0087] As the notch process, for example, the following methods can be given: a method of cutting notches in the discontinuous reinforcing fiber web by hand operation using a cutter or by a cutting machine, a method of pressing a rotating roller provided with a blade at a prescribed position against the discontinuous reinforcing fiber web, and the like. In the case of simply cutting notches in the discontinuous reinforcing fiber web, the former is suitable, while in the case of mass production with consideration of production efficiency, the latter is suitable. In the case of using a rotating roller, the blade can be provided at a prescribed position by directly cutting the roller and providing a blade, but it is preferable to wrap a flat plate cut out on a magnet roller or the like with a sheet-shaped mold in which a blade is provided at a prescribed position, so that the blade can be easily replaced.

[0088] The order of the impregnation process and the notch process can be either, but it is preferable to perform the notch process after the impregnation process, so that the reinforcing fibers are less likely to be detached from the blade, a stable quality can be obtained, and a prepreg can be manufactured with good productivity.

[0089] <Method for manufacturing fiber-reinforced plastic>

[0090] The molded substrate comprising the thermoplastic prepreg of the present application (hereinafter sometimes referred to as "molded substrate") can be used in a manufacturing method of fiber-reinforced plastic having a heating and pressurizing process in which the aforementioned thermoplastic resin is heated to be molten or softened and then pressurized. In other words, in the present specification, the material obtained by molding the molded substrate comprising the thermoplastic prepreg is referred to as "fiber-reinforced plastic". The molded substrate can comprise a material other than the thermoplastic prepreg of the present application, and can be a laminate in which other materials are laminated. The laminate can be integrated or not, but integration is preferable in order to prevent deterioration of surface quality and mechanical properties. As the molded substrate, it is more preferable to use a prepreg laminate comprising at least one or more thermoplastic prepregs of the present application. The respective contact surfaces of the laminated surfaces of the aforementioned prepreg laminate can be bonded to each other or not, but from the viewpoint of production efficiency, it is preferable that the surfaces are bonded to each other and the prepreg laminate is integrated. By integrated is meant a state in which the thermoplastic prepreg is bonded to the adjacent thermoplastic prepreg of the present application or other substrate. As the bonding method, for example, the entire or a part of the thermoplastic prepreg laminate can be heated to soften the thermoplastic resin, and then the thermoplastic resin can be cured by cooling to bond, or a bonding layer can be provided between the prepreg layers, and bonding can be performed via the components of the bonding layer. In the case where the other substrate comprises a thermosetting resin, bonding can be performed using the tackiness of the thermosetting resin.

[0091] By having the heating and pressurizing process, the thermoplastic resin contained in the aforementioned prepreg laminate is softened, and the discontinuous reinforcing fibers belonging to the aforementioned short fiber group, the discontinuous reinforcing fibers around the cutouts become easy to move and easily follow the complex shape at the time of pressurization. In order to be molten or softened, it is preferable to heat at a temperature of 10°C or more higher than the melting point or softening point of the thermoplastic resin, and specifically, it is preferable to heat at a temperature of 10°C or more higher than the melting point or softening point of the thermoplastic resin, and at a temperature of 10°C or less lower than the thermal decomposition temperature of the thermoplastic resin.

[0092] The manufacturing method of the reinforced fiber plastic in which the molding base material is deformed in a manner that the projected area in the thickness direction of the molding base material increases is preferable in the aforementioned heating and pressurizing step. Here, the projected area in the thickness direction refers to the projected area projected onto a plane perpendicular to the stacking direction of the prepreg laminate. A more specific example is that, in the hot press molding using the upper mold and the lower mold described later, the projected area projected onto the closing direction of the mold becomes the projected area in the thickness direction. In a state in which the thermoplastic resin contained in the molding base material is softened by heating the molding base material, and the cutouts are opened to become a state in which the molding base material is easily deformed, or in a state in which the discontinuous reinforcing fibers belonging to the aforementioned short fiber group are easily moved, by pressurizing the molding base material, the projected area in the thickness direction of the molding base material is increased compared to before the pressurization, so that the fiber reinforced plastic can be molded in correspondence with the increase in the area when the molding base material follows the unevenness of the mold surface. The measurement method of the projected area is not particularly limited, and for example, the following method can be mentioned: the images of the molding base material before molding and the fiber reinforced plastic after molding are photographed at the same angle and at the same magnification, and the areas of the molding base material and the fiber reinforced plastic are measured by removing the background using a general image processing software. More specifically, when the projected area in the thickness direction of the molding base material before the pressurization is set to S1, and the projected area after the pressurization is set to S2, the molding base material is preferably pressurized in a manner that S2 / S1 ≥ 1.6. By this means, the thermoplastic resin and the reinforcing fibers flow into the space formed due to the opening of the cutouts, and the voids from the cutout opening portions and the unevenness of the surface are suppressed, so it is preferable. More preferably, the range of S2 / S1 is 2.0 or more. In the molding process, from the viewpoint of suppressing the thermoplastic prepreg from being broken significantly, the upper limit of S2 / S1 is preferably 10.0.

[0093] The means for heating and pressurizing the molding base material is not particularly limited, and by using a mold for hot press molding, the fiber reinforced plastic can be produced at a good productivity, so it is preferable. Specifically, for example, the following method can be mentioned: the molding base material is arranged on either molding surface of the mold formed by the upper mold and the lower mold, the molding base material is heated to the vicinity of the molding temperature, and then the mold is closed to pressurize the molding base material and deform it along the molding surface shape of the mold. In the molding using hot press, the thickness direction coincides with the direction in which the mold moves when the molding base material is pressurized.

[0094] The heating temperature at the time of molding is not particularly limited, and in order to make the molding base material easily follow the molding surface shape of the mold, it is preferable to be equal to or higher than the melting point or the softening point of the thermoplastic resin contained in the prepreg.

[0095] Further, in order to obtain a fiber-reinforced plastic having high dimensional accuracy, a curing step can be further included in which, after the heating and pressurizing, the temperature of the mold is lowered in a state in which the upper and lower molds are closed, thereby curing the thermoplastic resin contained in the molded base material.

[0096] The prepreg of the present application can be used in a manufacturing method of a fiber-reinforced plastic having an expansion step and a curing step in this order, wherein the expansion step further reduces the pressure applied in the heating and pressurizing step to a pressure lower than the expansion pressure of the molded base material caused by the fuzzing force of the discontinuous reinforcing fibers, and the curing step cools the molded base material and cures the thermoplastic resin.

[0097] In the manufacturing method of a fiber-reinforced plastic of the present application, by having an expansion step, the thermoplastic prepreg of the present application is expanded by the fuzzing force of the discontinuous reinforcing fibers, and the density of the fiber-reinforced plastic when following a complex shape and being manufactured can be reduced, and a lightweight material can be obtained.

[0098] As a method of reducing the pressure applied in the heating and pressurizing step to a pressure lower than the expansion pressure of the molded base material caused by the fuzzing force of the discontinuous reinforcing fibers, a method of expanding the gap between the upper and lower molds after the heating and pressurizing step can be given. Further, a method of expanding the molded base material by unloading the pressure after the heating and pressurizing step can also be given. In this case, by confirming that the molded base material expands and the gap between the upper and lower molds increases after the pressure is unloaded, it can be confirmed that the pressure applied in the heating and pressurizing step is reduced to a pressure lower than the expansion pressure of the molded base material caused by the fuzzing force of the discontinuous reinforcing fibers.

[0099] In the manufacturing method of a fiber-reinforced plastic of the present application, by having a curing step, the shape of the molded base material expanded in the expansion step can be fixed, and a fiber-reinforced plastic having a complex shape and having lightweight and high mechanical properties can be obtained. The operation performed in the curing step is only required to fix the shape of the molded base material expanded in the expansion step, and is not limited, and specifically, a method of cooling the thermoplastic resin contained in the molded base material expanded in the expansion step to a temperature lower than the melting point or softening point can be given.

[0100] Further, a thickness adjustment step in which pressure is applied to the molded base material again to form a desired thickness can be further included between the expansion step and the curing step.

[0101] As a more preferable mode of the manufacturing method of a fiber-reinforced plastic of the present application, a manufacturing method using a thermoplastic prepreg in which, as the thermoplastic prepreg, the aforementioned characteristic (A) is satisfied, and the thermoplastic resin contained in the cut region in which the cut is formed is 0.5 to 2.0 g / m2 per 1 m2 of the cut region in the state before the cut is formed can be given.2 the sum of the lengths of the cutouts is set to X [m], and the maximum expansion ratio in the region other than the cutout region of the aforementioned thermoplastic prepreg determined by the following is set to Y, 5≤X / Y≤100 is satisfied.

[0102] Maximum expansion ratio Y: the thickness of a precursor obtained by taking out the region other than the cutout region from the aforementioned thermoplastic prepreg is set to P [mm], the thickness of a fiber-reinforced plastic obtained by keeping the aforementioned precursor at atmospheric pressure for 1 hour after heating the aforementioned precursor to a temperature at which the aforementioned thermoplastic resin is melted or softened in the aforementioned heating and pressurizing process is set to Q [mm], and the value obtained by Q / P.

[0103] As a specific method of measuring the maximum thermal expansion ratio Y, for example, the following method can be given: in the heating and pressurizing process, a precursor obtained by taking out the region other than the cutout region from the thermoplastic prepreg is arranged in a constant-temperature bath that is warmed to a temperature at which the thermoplastic resin is melted or softened, and is kept for 1 hour, and after a fiber-reinforced plastic is produced by swelling it by the fuzzing force of the discontinuous reinforcing fibers, the fiber-reinforced plastic is taken out of the constant-temperature bath, its thickness Q is measured using a vernier caliper or a micrometer, and Q / P is calculated using the thickness P of the precursor before swelling, which is measured in advance.

[0104] X becomes an index indicating the amount of the cutout formed in the cutout region, and has a tendency that the larger the value, the more the shape followability improves. Y becomes an index indicating the expansibility of the prepreg, and has a tendency that the larger the value, the more excellent the expansibility. By increasing the surface area in shape following, there is a tendency that the amount of the base material per unit area decreases, and the expansibility also decreases. That is, the shape followability and the expansibility have a tendency of trade-off, and in X and Y, which are indices thereof, if X is too large with respect to Y, the expansibility is poor, and it is difficult to obtain a fiber-reinforced plastic of a complex shape and light weight. On the other hand, if X is too small with respect to Y, although sufficient expansion is obtained, the shape followability is poor, and it is still difficult to obtain a fiber-reinforced plastic of a complex shape. A more preferable range of X / Y of the cutout region is 10≤X / Y≤80, and more preferably 20≤X / Y≤60.

[0105] < Fiber-reinforced plastic >

[0106] The fiber-reinforced plastic obtained by molding the thermoplastic prepreg of the present application typically has the following characteristics. That is, a fiber-reinforced plastic having a thermoplastic resin layer containing discontinuous reinforcing fibers and a thermoplastic resin, the aforementioned fiber-reinforced plastic satisfying at least one of the following characteristics (C) or (D),

[0107] Characteristic (C): there is an end portion alignment structure in which end portions of the aforementioned discontinuous reinforcing fibers oriented in three or more directions are continuously aligned in the aforementioned thermoplastic resin layer;

[0108] Feature (D): a fiber length variation portion having a coefficient of variation of fiber length of the discontinuous reinforcing fibers contained in the aforementioned thermoplastic resin layer of 40% or more.

[0109] The aforementioned end arrangement structure comes from the cutout provided in the thermoplastic prepreg of the present application, and thus, by its presence in the complex shape portion of the fiber-reinforced plastic, the reinforcing fibers do not become tight, and wrinkles and fiber disorder can be inhibited, and thus the surface quality is excellent.

[0110] The aforementioned fiber length variation portion comes from the fiber length variation region of the thermoplastic prepreg of the present application, and thus, by its presence in the complex shape portion of the fiber-reinforced plastic, the reinforcing fibers share the action according to the fiber length, and the shape followability and mechanical properties are excellent.

[0111] The thermoplastic resin layer can be present in at least a portion of the fiber-reinforced plastic, and is particularly preferably present in a portion having a complex shape. Note that in the present application, in the case where the fiber-reinforced plastic is formed from a single layer of the thermoplastic prepreg of the present application, it is also regarded as being present in the thermoplastic resin layer.

[0112] In the thermoplastic resin layer, in the case where the aforementioned expansion process is not performed at the time of molding the fiber-reinforced plastic, if the total of the volume content ratios of the discontinuous reinforcing fibers and the thermoplastic resin is 90% or more, then the fiber-reinforced plastic contains few gaps, and the mechanical properties are excellent, and thus it is preferable. The total of the volume content ratios of the discontinuous reinforcing fibers and the thermoplastic resin is more preferably 95% or more.

[0113] Here, the use of Figure 6 The end arrangement structure is described in detail. Figure 6Fig. 1 is a schematic view of the end arrangement structure periphery in the fiber reinforced plastic of the present application. The end arrangement of the reinforcing fibers refers to a state in which the distance between the ends of two reinforcing fiber filaments is in a relationship of 0.1 mm or less. That is, in the case where the end of a certain specific reinforcing fiber filament 18 is present within a circle 19 of a radius of 0.1 mm in the plane with the center of the end of the certain specific reinforcing fiber filament 18, it is considered that the end of the certain specific reinforcing fiber 18 is arranged with the end of another reinforcing fiber 20. By observing the cross section in the in-plane direction of the fiber reinforced plastic using a microscope, the line segment 21 between the ends of two reinforcing fiber filaments which are connected in different directions and which are in an arrangement relationship with each other is sequentially joined to form a line segment group 22, whereby the continuous arrangement of the reinforcing fiber ends can be confirmed. Here, in the case where the line segment group is formed of five or more line segments, it is considered that the continuous arrangement of the reinforcing fiber ends is present. Note that, in determining the line segment between the ends of two reinforcing fiber filaments, in the case where there are a plurality of ends of other reinforcing fiber filaments 20 which are arranged with the end of a certain specific reinforcing fiber filament 18, the end of the other reinforcing fiber filament 20 which is closest to the end of the certain specific reinforcing fiber filament 18 is selected, and the end of the other reinforcing fiber filament 20 for which the line segment has already been set is excluded from the options.

[0114] The aforementioned in-plane orientation of the reinforcing fiber group in different directions can be confirmed by the following method. First, the cross section in the in-plane direction of the fiber reinforced plastic is observed. Note that, in the case where the fiber reinforced plastic has a three-dimensional shape, a flat portion having a flat shape is selected in the fiber reinforced plastic, and the cross section in the in-plane direction (in other words, the direction perpendicular to the stacking direction) of the flat portion is observed. In the case where the aforementioned flat portion is not present in the fiber reinforced plastic, an observation region is set at an arbitrary position of the fiber reinforced plastic, and the cross section image captured using a camera and a microscope is observed from a direction perpendicular to the plane having the largest projected area of the observation region on the basis of the cross section of the thermoplastic resin layer belonging to the observation region being exposed. Then, one discontinuous reinforcing fiber is selected from the discontinuous reinforcing fiber group, and the in-plane orientation direction of the discontinuous reinforcing fiber is defined as the 0° direction. At this time, in the case where there is another discontinuous reinforcing fiber which crosses the discontinuous reinforcing fiber at an angle of 10° or more, it is judged that the discontinuous reinforcing fibers are oriented in different directions in the plane. Note that, "crossing" here means that, as in the case of the thermoplastic prepreg, the two discontinuous reinforcing fibers do not necessarily need to overlap in the thickness direction, and also includes the case where the extended lines obtained by extending each of the discontinuous reinforcing fibers in the orientation direction cross each other.

[0115] In the fiber-reinforced plastic of the present application, it is preferable that the aforementioned characteristic (C) be satisfied, and that the length of the aforementioned end arrangement structure be shorter than the average fiber length of the discontinuous reinforcing fibers contained in the thermoplastic resin layer. By having this form, a complex shape is obtained, and the surface quality is excellent, and damage caused by a cut can be suppressed, and the mechanical properties are excellent. Here, the length of the end arrangement structure refers to the length of the aforementioned line segment group that forms one end arrangement structure. From the viewpoint of strength, the length of the end arrangement structure is preferably short, and in particular, if it is longer than the average fiber length of the discontinuous reinforcing fibers, damage is sometimes easily generated from the end of the cut, and the mechanical properties decrease. It is more preferable that there be 10 or more of the aforementioned end arrangement structures on the surface of the fiber-reinforced plastic, and the average of the lengths of 10 of the aforementioned end arrangement structures selected at random therefrom be preferably shorter than the average fiber length of the discontinuous reinforcing fibers contained in the thermoplastic resin layer.

[0116] Next, the fiber length variation portion will be described. In the fiber-reinforced plastic of the present application, it is sufficient that a fiber length variation portion be present in at least a portion of the thermoplastic resin layer. Specifically, in the case where the thermoplastic resin layer contained in the fiber-reinforced plastic is divided into a plane in which the projected area of the fiber-reinforced plastic becomes the largest, and the area of the thermoplastic resin layer corresponding to the grid containing a square element of 50 mm x 50 mm in the plane, it is sufficient that the coefficient of variation of the fiber length in one or more of the aforementioned areas be 40% or more. In addition, in the present application, in the case of such division, the collection of the aforementioned areas in which the coefficient of variation of the fiber length is 40% or more is regarded as the "fiber length variation portion". The proportion of the fiber length variation portion in the thermoplastic resin layer is not particularly limited, and should be appropriately designed in accordance with the shape of the fiber-reinforced plastic, etc. In the present application, it is also possible that the entire thermoplastic resin layer be formed of a fiber length variation portion. Note that, in the case where the thermoplastic resin layer as the object does not satisfy the grid size, the entire thermoplastic resin layer is regarded as one aforementioned area. The method of measuring the fiber length of the reinforcing fibers contained in the thermoplastic resin layer can be measured by the method of measuring the reinforcing fibers contained in the aforementioned thermoplastic prepreg of the present application.

[0117] As a more preferable mode of the present application, it is more preferable to have a porous structure in which at least a portion of the contact points at which the aforementioned discontinuous reinforcing fibers cross each other are bonded by the aforementioned thermoplastic resin, and a void that is a portion in which neither the aforementioned discontinuous reinforcing fibers nor the aforementioned thermoplastic resin is present.

[0118] The mode of the thermoplastic resin and the discontinuous reinforcing fibers contained in the aforementioned porous structure is the same as the description relating to the aforementioned thermoplastic prepreg of the present application, and thus the description is omitted.

[0119] At least a part of the contact points of the discontinuous reinforcing fibers crossing each other is bonded by the thermoplastic resin, which means that the state in which the discontinuous reinforcing fibers crossing each other are bonded to each other via the thermoplastic resin can be confirmed by observing the surface of the porous structure with a microscope. By doing so, the network of the discontinuous reinforcing fibers included in the fiber-reinforced plastic of the present application, which is formed by the aforementioned thermoplastic resin, is lightweight and has excellent mechanical properties.

[0120] The voids, which are the portions in which neither the discontinuous reinforcing fibers nor the thermoplastic resin is present, can be confirmed by cross-sectional observation. Specifically, the cross section of the porous structure is taken, and after the cross section is polished, when the polished cross section is observed with a microscope, if a region in which neither the discontinuous reinforcing fibers nor the thermoplastic resin is present exists inside a closed curve formed by the discontinuous reinforcing fibers and the thermoplastic resin, the present requirement is satisfied. By doing so, the fiber-reinforced plastic having excellent lightweight properties is obtained.

[0121] In the porous structure of the present application, the void content is preferably in the range of 10% by volume or more and 99% by volume or less. The upper limit of the void content is preferably 97% by volume. Note that in the present application, the total of the volume contents of the thermoplastic resin, the discontinuous reinforcing fibers, and the voids included in the porous structure is taken as 100%. As a method for measuring the void content, there are a method in which a cross-sectional image of the porous structure of the present application is taken, and the total of the areas of the voids contained in the cross-sectional image is divided by the area of the entire cross-sectional image to calculate the void content, and a method in which the void content is calculated from the volume V1 of the laminate before molding and the volume V2 of the fiber-reinforced plastic after molding by (V2-V1) / V2x 100.

[0122] The fiber-reinforced plastic of the present application more preferably has the aforementioned end arrangement structure or the aforementioned fiber length variation portion at a complex shape portion. By doing so, the fiber-reinforced plastic having excellent dimensional accuracy at the complex shape portion is obtained. Here, the complex shape portion can be, for example, a region in which the thickness of the fiber-reinforced plastic changes, a region in which the surface is curved, a rib portion or a boss portion having a shape change in the direction away from the surface, or the like, but is not limited thereto as long as it has a three-dimensional structure.

[0123] Example

[0124] Hereinafter, the present application will be described in more detail by examples. However, the scope of the present application is not limited to these examples. Note that for evaluation, the number of measurements is 1 unless otherwise specified.

[0125] < Evaluation Method >

[0126] (1) Measurement of the orientation angle of the reinforcing fibers in the thermoplastic prepreg

[0127] The surface of the thermoplastic prepreg is observed with a microscope, and one reinforcing fiber filament is randomly selected. The two-dimensional orientation angle with respect to other reinforcing fiber filaments intersecting the reinforcing fiber filament is measured by image observation. The two-dimensional orientation angle is the angle (acute angle side) of 0° or more and 90° or less of the two angles formed by the intersecting two reinforcing fiber filaments. The number of measurements of each one two-dimensional orientation angle of the reinforcing fiber filaments is set to n = 20. Further, whether or not other discontinuous reinforcing fibers intersecting at an angle of 10° or more in the plane with respect to the orientation direction of the aforementioned randomly selected reinforcing fiber filament exist on the clockwise side and the counterclockwise side, respectively, is confirmed from the total of 20 measured two-dimensional orientation angles, and thus whether or not the discontinuous reinforcing fibers are oriented in three or more directions is determined.

[0128] In addition, the same measurement is performed on four reinforcing fiber filaments different from the above measurement, and in the case where the proportion of the two-dimensional orientation angle of 1° or more is 80% or more in the total of 100 measured two-dimensional orientation angles, the reinforcing fiber is determined to be monofilamentous. Further, in the case where the average value of the total of 100 measured two-dimensional orientation angles is in the range of 30° or more and 60° or less, the reinforcing fiber is determined to be randomly oriented.

[0129] (2) Measurement of weight proportion of thermoplastic resin and discontinuous reinforcing fiber

[0130] The weight of the discontinuous reinforcing fiber contained in the thermoplastic prepreg of 100 mm x 100 mm size is calculated from the weight per unit area of the discontinuous reinforcing fiber web produced according to the method described later. In addition, the weight of the thermoplastic prepreg of 100 mm x 100 mm is measured, and the weight of the thermoplastic resin is calculated by subtracting the weight of the discontinuous reinforcing fiber therefrom. The weight proportion of each is calculated from the weight of the discontinuous reinforcing fiber and the thermoplastic resin.

[0131] (3) Measurement of depth of cut

[0132] A cross-sectional image parallel to the thickness direction of the thermoplastic prepreg is photographed in such a manner that 10 or more cuts expose the cross section. Next, 10 cuts are randomly selected from the cuts exposed to the observation cross section, the depth of each cut is measured, and the average is calculated as the depth of the cut of the thermoplastic prepreg. In addition, the surface-to-surface distance of the discontinuous reinforcing fiber web is measured in the vicinity of the selected 10 cuts, and the average is calculated as the thickness of the discontinuous reinforcing fiber web. The calculation of (average of the depth of the cut) ÷ (average of the thickness of the discontinuous reinforcing fiber web) x 100 [%] is performed as the proportion of the depth of the cut of the present application. Note that in the case where the cut penetrates the discontinuous reinforcing fiber web, the depth of the cut and the thickness of the discontinuous reinforcing fiber web are the same value.

[0133] (4) Evaluation of the fiber length of the reinforcing fibers contained in the thermoplastic prepreg preform

[0134] A 50mm × 50mm thermoplastic prepreg blank was heated in air at 500°C for 1 hour to burn off the resin components. One hundred residual reinforcing fibers were randomly selected, and their lengths were measured using an optical microscope down to 1 μm. The average fiber length was calculated as the mean fiber length. Furthermore, based on the length data of the 100 fibers, the coefficient of variation of the fiber length was calculated, and a histogram with nine subgroups was plotted.

[0135] (5) Measurement of the sum of the incision lengths

[0136] The sum of the cut lengths of the thermoplastic prepreg blanks used in one example was measured and converted to a value per meter. 2 The numerical value of the length. The sum of the cut lengths of the two surfaces is measured, and the value of the surface with the larger sum of cut lengths is used.

[0137] (6) Measurement of elongation

[0138] Images of the pre-molded substrate and the post-molded fiber-reinforced plastic were acquired using a digital camera at the same magnification along the thickness direction. Next, image processing software was used to remove the background from the images, excluding the pre-molded substrate and fiber-reinforced plastic. The projected area S1 of the pre-molded substrate and the projected area S2 of the fiber-reinforced plastic were measured, and the value calculated as S2 / S1 was used as the elongation.

[0139] (7) Determination of the length of the end arrangement structure

[0140] The in-plane cross-section of the fiber-reinforced plastic is observed under a microscope, and the end of the reinforcing fiber near the opening of the cut is selected. Next, the ends with a distance of less than 0.1 mm are connected sequentially with line segments to form a line segment group. The length of the end arrangement structure is obtained by measuring the length of the line segment group.

[0141] (8) Molding test 1

[0142] Two 300mm x 300mm iron plates were used as upper and lower molds. The molds were heated to a surface temperature of 180°C. A molding substrate containing a thermoplastic prepreg was placed on the surface of the lower mold, and the upper mold was placed on top of the molding substrate. After holding this position for 30 seconds, the upper and lower molds were closed to apply the specified pressure as described in Table 1 to the molding substrate. After holding the molds closed for 5 minutes, the substrate was cooled and unloaded to obtain fiber-reinforced plastic.

[0143] (9) Molding test 2

[0144] Will Figure 7After the upper and lower molds having the shape of the molding surface described in Table 1 were warmed to a surface temperature of 180°C, the molding substrate of the present application was disposed on the surface of the lower mold, the upper mold was placed on the molding substrate and held for 30 seconds, and then the upper and lower molds were closed in a manner such that the molding substrate was subjected to a predetermined pressure described in Table 1. After the upper and lower molds were held in the closed state for 5 minutes, cooling and unloading were performed, and a fiber-reinforced plastic was obtained.

[0145] (10) Molding Test 3

[0146] After the upper and lower molds having the shape of the molding surface described in Table 1 were warmed to a surface temperature of 180°C, the molding substrate of the present application was disposed on the surface of the lower mold, the upper mold was placed on the molding substrate and held for 30 seconds, and then the upper and lower molds were closed in a manner such that the molding substrate was subjected to a predetermined pressure described in Table 1. After the upper and lower molds were held in the closed state for 5 minutes, cooling and unloading were performed, and a fiber-reinforced plastic was obtained. Figure 8 After the upper and lower molds having the shape of the molding surface described in Table 1 were warmed to a surface temperature of 180°C, the molding substrate of the present application was disposed on the surface of the lower mold, the upper mold was placed on the molding substrate and held for 30 seconds, and then the upper and lower molds were closed in a manner such that the molding substrate was subjected to a predetermined pressure described in Table 1. After the upper and lower molds were held in the closed state for 5 minutes, cooling and unloading were performed, and a fiber-reinforced plastic was obtained.

[0147] (11) Appearance Evaluation 1

[0148] The surface of the fiber-reinforced plastic obtained in the Molding Test 1 or the Molding Test 2 was visually confirmed, and the surface state was evaluated in four levels of A, B, C, and D described below. Note that the fiber-reinforced plastic surface has a high surface quality in the order of A, B, C, and D. In addition, for the fiber-reinforced plastic having an elongation of 1.0 or less, it was considered that the complex shape was not followed, and the appearance evaluation was not performed.

[0149] A: The opening portion of the notch was not obvious, and had a good surface quality.

[0150] B: The opening portion of the notch was observed, but the opening portion was not connected, and had a good surface quality.

[0151] C: The opening portion of the notch was partially connected, but the length of the end portion arrangement structure was less than the average fiber length.

[0152] D: The opening portion of the notch was connected, and had a large damage having a length of the end portion arrangement structure of the average fiber length or more.

[0153] (12) Appearance Evaluation 2

[0154] The surface of the fiber-reinforced plastic obtained in the moldability test 3 was visually confirmed, and the surface state was evaluated in the following four grades of A, B, C, and D shown below. Note that the fiber-reinforced plastic had a high surface quality in the order of A, B, C, and D.

[0155] A: Follows the concave-convex shape, and the cut is not obvious, and a good surface quality is obtained.

[0156] B: Follows the concave-convex shape, but the cut is slightly observed by visual observation.

[0157] C: Follows the concave-convex shape, but the cut is easily observed by visual observation.

[0158] D: Does not follow the concave-convex shape, and a large damage is observed.

[0159] (13) Evaluation of mechanical properties

[0160] A rectangular test piece of 10 mm in width and 100 mm in length was cut out from the fiber-reinforced plastic obtained in the moldability test 1, and a three-point bending test was performed in accordance with JIS K 7074 (1988) to measure the bending strength and the bending modulus.

[0161] (14) Measurement of expansion ratio

[0162] A 50 mm x 50 mm size of the aforementioned cut region or the aforementioned fiber length variation region was cut out from the thermoplastic prepreg, the thicknesses of three positions were measured using a micrometer, and the average thereof was taken as the thickness R of the thermoplastic prepreg before heating. Next, the thermoplastic prepreg was expanded by being left in a thermostat tank in which the atmosphere temperature was set to 180°C for 1 hour, the thicknesses of three positions were measured using a micrometer, and the average thereof was taken as the thickness S of the fiber-reinforced plastic, and the expansion ratio was measured from S / R.

[0163] (15) Measurement of maximum expansion ratio

[0164] A 50 mm x 50 mm size of the thermoplastic prepreg before the cut was inserted in the example was cut out, the thicknesses of three positions were measured using a micrometer, and the average thereof was taken as the thickness P [mm] of the thermoplastic prepreg. Next, the thermoplastic prepreg was expanded by being left in a thermostat tank in which the atmosphere temperature was set to 180°C for 1 hour, and a fiber-reinforced plastic was obtained. The fiber-reinforced plastic was taken out, the thicknesses of three positions were measured using a micrometer, and the average thereof was taken as the thickness Q [mm] of the fiber-reinforced plastic. Q / P was calculated using the measured P and Q, and the maximum expansion ratio Y was obtained.

[0165] (16) Evaluation of shape

[0166] In the fiber-reinforced plastic obtained in the moldability test 3, attention was paid to the fiber-reinforced plastic in which the cut was not observed by visual observation. Figure 8(a) shows the surface of the side in contact with the lower mold. The quality of the angle at shape evaluation position 23 is evaluated using four levels: A, B, C, and D, as shown below. It should be noted that the corner of the lower mold is a right angle, and the mold shape reproduction is evaluated in the order of A, B, C, and D, indicating excellent dimensional accuracy.

[0167] A: It has a vertical angle that is the same as the shape of the mold.

[0168] B: Corners with a radius of less than 1 mm.

[0169] C: A corner with a small circle having a radius of 1 mm or more but less than 3 mm.

[0170] D: A corner with a large circle having a radius of 3mm or more.

[0171] (17) Density

[0172] A rectangular test piece measuring 10 mm × 10 mm × the thickness of the fiber-reinforced plastic [mm] was cut from the fiber-reinforced plastic obtained in molding test 3. The longitudinal, transverse, and thickness of the test piece were measured using a micrometer, and the volume V [mm²] of the test piece was calculated from the obtained values. 3 In addition, the mass M [g] of the test piece used for the test was measured using an electronic balance. The density ρ of the fiber-reinforced plastic was calculated by substituting the obtained mass M and volume V into the following formula.

[0173] ρ[g / cm 3 ] = 10 3 ×M[g] / V[mm 3 ].

[0174] (Example 1)

[0175] [Thermoplastic resin sheet (1)]

[0176] A sample containing 50% by weight of unmodified polypropylene resin (Prime Polymer Co., Ltd. "Primepolypro" (registered trademark) J105G) and 50% by weight of acid-modified polypropylene resin (Mitsui Chemicals Co., Ltd. "Admer" QB510) with a unit area weight of 100 g / m² was prepared. 2 Thermoplastic resin sheet (1).

[0177] [Discontinuous reinforced fiber web (1)]

[0178] The reinforcing fiber (1) (a continuous PAN-based carbon fiber bundle with a tensile strength of 4900 MPa, a tensile modulus of 230 GPa, and a total of 12,000 monofilaments) was cut into 6 mm pieces using a cartridge cutter to obtain discontinuous reinforcing fibers.

[0179] A dispersion liquid having a concentration of 0.1% by weight was prepared from water and a surfactant (Polyoxyethylene Lauryl Ether (trade name) manufactured by Nacalai Tesque, Inc.).

[0180] A discontinuous reinforcing fiber web (1) was produced using the dispersion liquid and the above discontinuous reinforcing fiber using a discontinuous reinforcing fiber web production apparatus.

[0181] The discontinuous reinforcing fiber web production apparatus has a dispersion tank having a cylindrical shape with a diameter of 1000 mm having an opening cock at the lower portion, and a papermaking tank, and is provided with a linear-shaped conveyance portion (inclination angle 30°) connecting the dispersion tank and the papermaking tank. A stirrer is attached to the opening portion of the upper surface of the dispersion tank, and the discontinuous reinforcing fiber and the dispersion liquid (dispersion medium) can be fed from the opening portion. The papermaking tank is a tank provided with a web belt conveyer having a papermaking surface with a width of 500 mm at the bottom portion, and the conveyer capable of transporting the papermaking base material is connected to the web belt conveyer.

[0182] The papermaking was performed so that the concentration of the discontinuous reinforcing fiber in the dispersion liquid was 0.05% by weight. The discontinuous reinforcing fiber after the papermaking was dried in a drying oven at 200°C for 30 minutes. The obtained discontinuous reinforcing fiber web (1) had a width of 500 mm, a length of 500 mm, and a weight per unit area of 100 g / m 2 .

[0183] [Resin-impregnated base material (1)]

[0184] The resin-impregnated base material (1) in which the thermoplastic resin was impregnated in the discontinuous reinforcing fiber web (1) was produced using the discontinuous reinforcing fiber web (1) and the thermoplastic resin sheet (1) by stacking in the order of [thermoplastic resin sheet (1) / discontinuous reinforcing fiber web (1) / thermoplastic resin sheet (1)], and applying a pressure of 5 MPa for 2 minutes at a temperature of 230°C.

[0185] The resin-impregnated base material (1) was pressed against a rotary blade provided with a blade edge at a prescribed position, whereby a cut having a regular pattern shown in (b) was inserted in such a manner that the total length of the cuts was 100 m on both the front and back surfaces per 1 m 2 . Figure 3 of the thermoplastic prepreg. The cuts were provided in such a manner that they covered the entire surface of the thermoplastic prepreg, and the depth of the cuts reached a position of 60% of the thickness of the discontinuous reinforcing fiber web.

[0186] When the above-described <Evaluation Method> (1) was used to measure the fiber orientation direction in the plane of the thermoplastic prepreg based on the measurement of the orientation angle of the reinforcing fibers in the thermoplastic prepreg, it was confirmed that the discontinuous reinforcing fibers were oriented in three or more directions. In addition, the proportion of the two-dimensional orientation angle of the thermoplastic prepreg that was 1° or more was 90%. Furthermore, the average of the two-dimensional orientation angle was 40°. That is, the reinforcing fibers were single fibers, and were randomly oriented.

[0187] In addition, when the above-described (2) was used to measure the weight proportion of the thermoplastic resin and the discontinuous reinforcing fibers contained in the thermoplastic prepreg, the thermoplastic resin was 67% by weight, and the discontinuous reinforcing fibers were 33% by weight.

[0188] A molding test 1 was performed using a molding base material in which the thermoplastic prepreg was cut to a size of 100 mm x 100 mm and integrated after being laminated in four sheets, with heating in a constant-temperature tank at 140°C and pressurization at a pressure of 1 MPa.

[0189] In addition, a molding test 2 was performed using a molding base material in which the thermoplastic prepreg was cut to a size of 150 mm x 150 mm and integrated after being laminated in four sheets.

[0190] (Example 2)

[0191] A molding test 1 was performed using a molding base material in which the thermoplastic prepreg was cut to a size of 100 mm x 100 mm and integrated after being laminated in four sheets, with heating in a constant-temperature tank at 140°C and pressurization at a pressure of 1 MPa.

[0192] The fiber length distribution of the discontinuous reinforcing fibers contained in the thermoplastic prepreg was obtained according to the above-described (4), and a histogram of the fiber length was prepared. The coefficient of variation of the fiber length, the group with the highest frequency in the prepared histogram, and the number of groups with a frequency of 10% or more are shown in Table 1, respectively.

[0193] A molding test 3 was performed using a molding base material in which the thermoplastic prepreg was cut to a size of 100 mm x 100 mm and integrated after being laminated in four sheets, with heating in a constant-temperature tank at 140°C and pressurization at a pressure of 1 MPa.

[0194] (Example 3)

[0195] A molding test 1 was performed using a molding base material in which the thermoplastic prepreg was cut to a size of 100 mm x 100 mm and integrated after being laminated in four sheets, with heating in a constant-temperature tank at 140°C and pressurization at a pressure of 1 MPa.

[0196] (Example 4)

[0197] The number of cuts was converted to 1 m 2The slits are inserted in such a way that the sum of the slit lengths on both the front and back sides is 20m. Otherwise, the thermoplastic prepreg blank is made in the same way as in Example 2, and the molding test 1 and molding test 3 are carried out.

[0198] (Example 5)

[0199] Converted to per 1m 2 The slits are inserted in such a way that the sum of the slit lengths on both the front and back sides is 40m. Otherwise, the thermoplastic prepreg blank is made in the same way as in Example 2, and the molding test 1 and molding test 3 are carried out.

[0200] (Example 6)

[0201] Converted to per 1m 2 The slits are inserted in such a way that the sum of the slit lengths on both the front and back sides is 400m. Otherwise, the thermoplastic prepreg blank is made in the same way as in Example 2, and the molding test 1 and molding test 3 are carried out.

[0202] (Example 7-1)

[0203] Converted to per 1m 2 The slits are inserted in such a way that the sum of the slit lengths on both the front and back sides is 200m. Otherwise, the thermoplastic prepreg blank is made in the same way as in Example 2, and the molding test 1 and molding test 3 are carried out.

[0204] (Example 7-2)

[0205] Using the thermoplastic prepreg blank prepared in Example 7-1, a molding substrate was made without integral bonding after lamination, and a molding test 1 was conducted using the molding substrate.

[0206] (Example 7-3)

[0207] [Thermosetting prepreg blank]

[0208] Epoxy resin (Epikote 828 manufactured by Japan Epoxy Resin Co., Ltd.: 40 parts by weight, Epikote 1007FS manufactured by Japan Epoxy Resin Co., Ltd.: 25 parts by weight, EPICLON N740 manufactured by DIC Co., Ltd.: 35 parts by weight) and thermoplastic resin polyvinyl alcohol formaldehyde (VINYLEC K manufactured by CHISSO Co., Ltd.: 3 parts by weight) were added to a beaker, heated to 80°C, and mixed for 30 minutes.

[0209] After the resin temperature was lowered to 30°C, 3.5 parts by mass of a curing agent, dicyandiamide (DICY7 manufactured by Japan Epoxy Resin (K.K.) and 2 parts by mass of a curing accelerator, 2,4-toluene bis(dimethylurea) ("OMICURE (registered trademark)" 24 manufactured by PTI Japan (K.K.)) were added, and after stirring for 10 minutes, the kneader was removed to obtain an epoxy resin composition.

[0210] The obtained epoxy resin composition was coated on a release paper coated with silicone having a thickness of 100 μm using a reverse roll coater to produce a thermosetting resin sheet (1) at 29 g / m 2 .

[0211] A reinforcing fiber (1) was arranged in one direction on a sheet, and a thermosetting resin sheet (1) was overlaid from both sides of the sheet, and the resin composition was impregnated by heating and pressing to produce a unidirectionally arranged thermosetting prepreg (1) having a reinforcing fiber unit area weight of 100 g / m 2 and a reinforcing fiber content of 63% by weight.

[0212] The same thermosetting prepreg (1) as the thermoplastic prepreg was arranged on both the upper and lower surfaces of the same molding base material as in Example 7-1, and molding property test 1 was performed. At this time, the fiber orientation directions of the thermosetting prepregs (1) on both surfaces were in the same direction.

[0213] As a result, the elongation was 1.8, and the surface quality had "A" in the appearance evaluation. However, only the projected area of the thermoplastic prepreg was clearly increased, and the projected area of the thermosetting prepreg (1) was hardly changed before and after pressing. In addition, the results of the mechanical evaluation were a bending strength of 1200 MPa and a bending modulus of 90.0 GPa. Note that in the mechanical property evaluation, the test piece was produced in such a manner that the fiber orientation direction of the thermosetting prepreg (1) of the surface layer was along the length direction of the test piece.

[0214] (Example 8)

[0215] A cut was inserted in such a manner that the sum of the cut lengths per 1 m 2 became 800 m on both the front and back surfaces, and a thermoplastic prepreg was produced in the same manner as in Example 2, and molding property test 1, molding property test 3 were performed.

[0216] (Comparative Example 1)

[0217] A cut was not inserted in the resin-impregnated base material (1), and it was directly used as a thermoplastic prepreg, and molding property test 1 and molding property test 2, molding property test 3 were performed.

[0218] The results of the constitution and formability test of the thermoplastic prepreg produced in each of the examples and comparative examples are shown in Table 1.

[0219] Table 1-1

[0220]

[0221] Table 1-2

[0222]

[0223] Explanation of Reference Signs

[0224] 1: notch

[0225] 2: notch region

[0226] 3: thermoplastic prepreg

[0227] 4: discontinuous reinforcing fiber web

[0228] 5: surface of one side into which notch 1 is inserted

[0229] 6: surface of the opposite side of the surface into which notch 1 is inserted

[0230] 7: leading end of notch

[0231] 8: depth of notch

[0232] 9: thickness of discontinuous reinforcing fiber web

[0233] 10: notch unit

[0234] 11: group with the highest frequency

[0235] 12: group with a fiber length shorter than the group with the highest frequency

[0236] 13: long fiber group

[0237] 14: group with a fiber length shorter than the group with the highest frequency

[0238] 15: short fiber group

[0239] 16: reinforcing fiber filament

[0240] 17: two-dimensional orientation angle

[0241] 18: specific reinforcing fiber filament

[0242] 19: circle centered on the end of the specific reinforcing fiber filament

[0243] 20: other reinforcing fiber filament

[0244] 21: line segment

[0245] 22: group of line segments

[0246] 23: shape evaluation position

[0247] 24: lower mold

[0248] 25: upper mold

[0249] 26: fiber-reinforced plastic

[0250] 27: radius of corner

Claims

1. A thermoplastic prepreg preform, which is formed by impregnating a thermoplastic resin with a discontinuous reinforcing fiber web, said thermoplastic prepreg preform satisfying the following characteristic (A), Feature (A): has a plurality of cuts that sever at least a portion of the discontinuous reinforcing fibers constituting the discontinuous reinforcing fiber web. The cut is a cut that reaches a depth of 100% in the thickness direction of the discontinuous reinforcing fiber web, and the length of the cut is less than 50 mm.

2. The thermoplastic prepreg blank as claimed in claim 1, comprising: 40% to 90% by weight of the thermoplastic resin and 10% to 60% by weight of the discontinuous reinforcing fiber.

3. The thermoplastic prepreg preform as described in claim 1, wherein, Thermoplastic prepreg preforms also meet the following characteristics (B), Feature (B): A region of fiber length variation in which the coefficient of variation of the fiber length of the discontinuous reinforcing fibers constituting the discontinuous reinforcing fiber web is 40% or more.

4. The thermoplastic prepreg blank according to any one of claims 1 to 3, wherein, The cuts are arranged regularly.

5. The thermoplastic prepreg blank according to any one of claims 1 to 3, wherein, The average fiber length of the discontinuous reinforcing fiber is in the range of 2 mm to 20 mm.

6. The thermoplastic prepreg blank according to any one of claims 1 to 3, wherein, The conversion within the cut area where the aforementioned cuts are formed is per 1m. 2 The total length of the cuts is over 40m.

7. The thermoplastic prepreg blank according to any one of claims 1 to 3, wherein, The conversion within the cut area where the aforementioned cuts are formed is per 1m. 2 The total length of the cuts is between 40m and 500m.

8. The thermoplastic prepreg blank as described in claim 3, wherein, In the region of fiber length variation, when a histogram representing the fiber length distribution of the discontinuous reinforcing fibers is constructed under the following conditions, the highest frequency is 70% or less. Conditions: Measure the length of discontinuous reinforcing fibers randomly selected from the discontinuous reinforcing fibers contained in the fiber length variation region by dividing the range from the minimum to the maximum fiber length equally into 9 groups to create a histogram with 9 groups; when the number of the randomly selected discontinuous reinforcing fibers is taken as 100%, the frequency is set as the percentage of the number of discontinuous reinforcing fibers belonging to each group [%).

9. The thermoplastic prepreg preform as described in claim 8, wherein, In the histogram, there are more than three groups with a frequency of 10% or higher.

10. The thermoplastic prepreg blank according to any one of claims 1 to 3, wherein, When the thickness of the precursor obtained by cutting only the region with the plurality of cuts or the region with the variation in fiber length from the thermoplastic prepreg is defined as R [mm], and the thickness of the fiber-reinforced plastic obtained by heating the precursor to a temperature above that melts or softens the thermoplastic resin and holding the precursor at atmospheric pressure for 1 hour is defined as S [mm], the expansion ratio calculated from S / R is 2.0 or higher.

11. The thermoplastic prepreg preform as described in claim 3, wherein, Multiple cuts are formed in the fiber length variation region to cut at least a portion of the reinforcing fibers contained in the discontinuous reinforcing fiber web.

12. The thermoplastic prepreg blank according to any one of claims 1 to 3, wherein, The discontinuous reinforcing fibers are in the form of single fibers.

13. The thermoplastic prepreg blank according to any one of claims 1 to 3, wherein, The discontinuous reinforcing fibers are randomly oriented in the plane.

14. A fiber-reinforced plastic, which is formed by molding a thermoplastic prepreg blank according to any one of claims 1 to 13, either alone or by stacking two or more sheets.

15. A method for manufacturing a thermoplastic prepreg preform, comprising the method of manufacturing the thermoplastic prepreg preform according to any one of claims 1 to 13, the method comprising: The web-making process involves producing discontinuous reinforcing fiber webs. The impregnation process involves impregnating a discontinuous reinforcing fiber web with thermoplastic resin; The cutting process involves inserting multiple cuts in a manner that cuts at least a portion of the discontinuous reinforcing fibers constituting the discontinuous reinforcing fiber web.

16. A method for manufacturing fiber-reinforced plastics, comprising a heating and pressurizing process, wherein, The molding substrate comprising the thermoplastic prepreg blank according to any one of claims 1 to 13 is pressurized while the thermoplastic resin is heated to melt or soften it.

17. The method for manufacturing fiber-reinforced plastic as described in claim 16, wherein, In the heating and pressurizing process, the molding substrate is deformed in such a way that the projected area in the thickness direction of the molding substrate is increased.

18. The method for manufacturing fiber-reinforced plastic as described in claim 17, wherein, When the projected area in the thickness direction of the molded substrate before pressurization is set as S1 and the projected area after pressurization is set as S2, the molded substrate is pressurized in such a way that S2 / S1≥1.

6.

19. The method for manufacturing fiber-reinforced plastic as described in claim 16, comprising, in sequence: The expansion process further reduces the pressure applied in the heating and pressurizing process to below the expansion pressure of the molded substrate caused by the napping force of the discontinuous reinforcing fibers; The curing process involves cooling the molded substrate and curing the thermoplastic resin.

20. The method for manufacturing fiber-reinforced plastic as described in claim 16, wherein, As the thermoplastic prepreg blank, the following thermoplastic prepreg blank is used: satisfying the above feature (A), and converting the area in which the cut is formed to per 1m 2 When the sum of the cut lengths is set as X [m], and the maximum expansion rate in the region outside the cut area of ​​the thermoplastic prepreg blank, as determined below, is set as Y, then 5 ≤ X / Y ≤ 100 is satisfied. Maximum expansion rate Y: The thickness of the precursor obtained by removing the area outside the cut region from the thermoplastic prepreg blank is set as P [mm], and the thickness of the fiber-reinforced plastic obtained by heating the precursor to a temperature that melts or softens the thermoplastic resin in the heating and pressurizing process and then holding the precursor at atmospheric pressure for 1 hour is set as Q [mm]. The value is obtained by Q / P.

21. A fiber-reinforced plastic, which is formed by molding a thermoplastic prepreg preform according to any one of claims 1 to 13, having a thermoplastic resin layer comprising discontinuous reinforcing fibers and thermoplastic resin, said fiber-reinforced plastic satisfying at least one of the following characteristics (C) or (D). Feature (C): The thermoplastic resin layer contains an end-arrangement structure in which the ends of the discontinuous reinforcing fibers oriented in more than three directions are continuously arranged. Feature (D): The fiber length variation portion of the discontinuous reinforcing fibers contained in the thermoplastic resin layer has a coefficient of variation of 40% or more.

22. The fiber-reinforced plastic of claim 21, having a porous structure in which at least a portion of the contact points where the discontinuous reinforcing fibers intersect are bonded by the thermoplastic resin, and includes voids as portions where neither the discontinuous reinforcing fibers nor the thermoplastic resin are present.

23. The fiber-reinforced plastic of claim 22, wherein it satisfies the aforementioned feature (C), The end arrangement structure exists inside the porous structure, and the length of the end arrangement structure is shorter than the average fiber length of the discontinuous reinforcing fibers.

24. The fiber-reinforced plastic according to any one of claims 21 to 23, wherein it satisfies the aforementioned feature (C), The length of the end arrangement structure is shorter than the average fiber length of the reinforcing fibers.

25. The fiber-reinforced plastic according to any one of claims 21 to 23, wherein it satisfies the aforementioned feature (D). In the portion of fiber length variation, when a histogram representing the fiber length distribution of the discontinuous reinforcing fibers is generated under the following conditions, the highest frequency is 70% or less. Conditions: Measure the length of discontinuous reinforcing fibers randomly selected from the discontinuous reinforcing fibers included in the fiber length variation section, by equally dividing the range from the minimum fiber length to the maximum fiber length into 9 parts to create a histogram with 9 groups; when the number of the randomly selected discontinuous reinforcing fibers is taken as 100%, the frequency is set as the percentage of the number of discontinuous reinforcing fibers belonging to each group [%).

26. The fiber-reinforced plastic of claim 25, wherein, In the histogram, there are more than three groups with a frequency of 10% or higher.

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