Random sheet manufacturing method and random sheet

Abstract

To provide a method for manufacturing a random sheet having higher bending stress and bending elastic modulus.SOLUTION: A method for manufacturing a random sheet includes the steps of planarly spreading chips of a fiber-reinforced resin, and heating and pressing the spread chips, and integrating the chips. The chip has an aspect ratio (L / W) that is a ratio of a length (L) to a width (W) of 2 or more and 10 or less, and the chip is obtained by impregnating a plurality of reinforcement fibers oriented in the same direction and aligned with a matrix resin, and has one or more and 8 or less chip-shaped bent parts formed by bending the reinforcement fibers.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a random sheet and a random sheet. [Background technology]

[0002] A thin-film fiber-reinforced resin (hereinafter simply referred to as a "Uni-Direction (UD) sheet") is known, which contains a plurality of reinforcing fibers oriented in one direction and a resin composition (matrix resin) impregnated into the reinforcing fibers. This UD sheet is cut into thin pieces, which are then randomly arranged in a two-dimensional pattern and heated and pressurized to form a sheet. This produces a random sheet, in which blocks of reinforcing fibers oriented in one direction are randomly arranged (see, for example, Patent Document 1). Random sheets have a unique marble-like appearance and are highly moldable (shapeable) by stamp molding, press molding, and other processes, and are therefore expected to be used in a variety of applications. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-210417 Summary of the Invention [Problem to be solved by the invention]

[0004] According to the findings of the present inventors, a random sheet has higher formability but lower bending stress and bending modulus than a UD sheet.

[0005] The present invention has been made in consideration of the above problems, and its object is to provide a method for producing a random sheet having a higher bending stress and bending modulus, and a random sheet having an increased bending modulus. [Means for solving the problem]

[0006] A method for manufacturing a random sheet according to one embodiment of the present invention for solving the above problems includes the steps of laying fiber-reinforced resin chips in a flat plane and heating and pressurizing the laid chips to integrate the chips. The chips have an aspect ratio (L / W), which is the ratio of length (L) to width (W), of 2 to 10, and are formed by impregnating a matrix resin with a plurality of reinforcing fibers aligned in the same direction, and have one to eight bends where the shape of the chips and the reinforcing fibers are bent.

[0007] Another embodiment of the present invention for solving the above problems provides a random sheet comprising a plurality of chips laid out in a plane and integrated under heat and pressure. The chips have an aspect ratio (L / W), which is the ratio of length (L) to width (W), of 2 to 10. The chips are composed of a plurality of reinforcing fibers aligned in the same direction and impregnated with a matrix resin, and have one to eight bends.

[0008] Another embodiment of the present invention provides a random sheet in which a plurality of chips are laid out in a planar manner and integrated by heating and pressurizing, and the standard deviation of the fiber orientation distribution in the thickness direction of the random sheet is 30 or more. [Effects of the Invention]

[0009] According to the present invention, a method for producing a random sheet having a higher bending stress and bending modulus, and a random sheet having an increased bending modulus are provided. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a flowchart showing a method for manufacturing a random sheet according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing the structure of chopped chips used in manufacturing a random sheet. [Figure 3] FIG. 3A is a schematic diagram showing chopped chips having an odd number of bent portions, and FIG. 3B is a schematic diagram showing chopped chips having two bent portions. [Figure 4] FIG. 4 is a schematic diagram showing how chopped chips are produced by passing a UD sheet through a pair of rollers. DETAILED DESCRIPTION OF THE INVENTION

[0011] 1. Manufacturing method of random sheets Fig. 1 is a flowchart showing a method for manufacturing a random sheet according to one embodiment of the present invention. As shown in Fig. 1, the manufacturing method according to this embodiment includes a step of laying out chips of fiber-reinforced resin (step S110) and a step of integrating the chips by applying heat and pressure (step S120).

[0012] 1-1. Spreading process (step S110) In the first step, fiber-reinforced resin chips are laid out in two dimensions.

[0013] 1-1-1. Fiber reinforced resin chips 1-1-1―1. Chip configuration The fiber-reinforced resin chips (hereinafter simply referred to as "chopped chips") are fiber-reinforced resin chips formed by impregnating a matrix resin into a plurality of reinforcing fibers aligned in the same direction. The chopped chips are elongated chips with an aspect ratio (L / W), which is the ratio of length (L) to width (W), of 2 to 10. The chopped chips have one to eight bends in the shape of the chip and where the reinforcing fibers are bent.

[0014] FIG. 2 is a schematic diagram showing the configuration of chopped chips used to manufacture a random sheet in this embodiment. As shown in FIG. 2, chopped chips 110 are fiber-reinforced resin chips formed by impregnating a matrix resin 114 with a plurality of reinforcing fibers 112 oriented in one direction and arranged parallel to one another. Chopped chips 110 have bent portions 116a, 116b, 116c, and 116d. Note that while FIG. 2 shows the bent reinforcing fibers 112 as existing in the same plane, they may also be bent in the depth direction of the figure.

[0015] The aspect ratio (L / W) of the chopped chips 110, which is the ratio of the length (L) to the width (W), is 2 or more and 10 or less. In this specification, the length (L) of the chopped chips 110 means the shortest distance connecting the ends of the chopped chips 110 in the arranging direction of the reinforcing fibers 112. Furthermore, the width (W) of the chopped chips 110 means the distance between the ends of the chopped chips 110 in a direction perpendicular to the arranging direction of the reinforcing fibers 112. When the width of the chopped chips 110 varies from part to part, the maximum value of these is defined as the width (W) of the chopped chips 110. When the peripheral portion of the chopped chips 110 has an irregular shape and multiple ends for measuring the length (L) or width (W) can be set in one chopped chip 110, the distance between the ends that makes the length (L) or width (W) longest can be set as the length (L) and width (W).

[0016] The chopped chips 110 are elongated chips with a large aspect ratio (L / W). The chopped chips 110 have bent portions. In this process, by laying out such elongated and bent chips on a plane, the chips can be laid out more randomly and the reinforcing fibers 112 can be easily laid out so that they are oriented in the depth direction. In particular, by using the elongated and bent chips, the bent portions can easily enter between other chips, making it easier to lay out the reinforcing fibers 112 so that they are oriented in the depth direction. Therefore, in the molded random sheet, the orientation direction of the reinforcing fibers 112 can be made more random, and more reinforcing fibers 112 can be oriented in the depth direction as well. As a result, the bending resistance (bending stress, bending modulus, etc.) of the random sheet can be further improved.

[0017] By setting the aspect ratio (L / W) to 2 or more, it is possible to easily form bent portions in the chopped chips 110. Furthermore, by setting the aspect ratio (L / W) to 2 or more, it is possible to easily orient the reinforcing fibers 112 in the depth direction when the chopped chips 110 are laid out. On the other hand, by setting the aspect ratio (L / W) to 10 or less, it is possible to make the chopped chips 110 less likely to curl up when laid out, and it is possible to easily orient the reinforcing fibers 112 in the depth direction. From the above viewpoint, the aspect ratio of the chopped chips 110 is preferably 2 or more and 8 or less, and more preferably 3 or more and 6 or less.

[0018] In addition, from the viewpoint of making it easier to orient the reinforcing fibers 112 in the depth direction, the length (L) of the chopped chips 110 is preferably 5 mm or more and 70 mm or less, more preferably 8 mm or more and 50 mm or less, and even more preferably 10 mm or more and 30 mm or less.

[0019] From the viewpoint of facilitating the orientation of the reinforcing fibers 112 in the depth direction, the width (W) of the chopped chips 110 is preferably 5 mm or less, and more preferably 1 mm or more and 4 mm or less.

[0020] Furthermore, from the viewpoint of facilitating the orientation of the reinforcing fibers 112 in the depth direction, the thickness of the chopped chips 110 is preferably 50 μm or more and 1000 μm or less, and more preferably 100 μm or more and 500 μm or less. In this specification, the thickness of the chopped chips 110 means the distance between the ends of the chopped chips 110 in a direction perpendicular to both the orientation direction of the fibers and the width direction at the thickness measurement position.

[0021] The chopped chips 110 preferably have a curvature (L / EL), which is the ratio of the length (L) to the stretched length (EL) of the chopped chips, of 0.50 to 0.90, more preferably 0.60 to 0.85, and even more preferably 0.65 to 0.80. When the curvature is within the above range, the orientation direction of the reinforcing fibers 112 in the random sheet can be made more random, and more reinforcing fibers 112 can be easily oriented in the depth direction as well. The stretched length (EL) of the chopped chips 110 refers to the length of the chopped chips 110 when the chopped chips 110 are not bent. The stretched length (EL) of the chopped chips 110 can be determined by measuring the length of the chopped chips 110 in a bent state along the reinforcing fibers 112.

[0022] Furthermore, the more bent portions there are, the more easily the bent portions can get between other chips, making it easier to orient the reinforcing fibers 112 in the depth direction when the chopped chips 110 are laid out. On the other hand, by limiting the number of bent portions to eight or less, it is possible to suppress a decrease in the strength of the random sheet caused by the chopped chips 110 being broken and shortened during pressing. From the above perspective, the number of bent portions that the chopped chips 110 have is preferably two to seven, and more preferably three to six.

[0023] The above length (L), width (W), thickness, aspect ratio, maximum length (EL) of the reinforcing fiber 112, and number of bends can be calculated as the average of these values ​​measured for 100 randomly selected chopped chips 110.

[0024] Furthermore, from the viewpoint of increasing the entanglement of the chopped chips 110 and making it easier to orient the reinforcing fibers 112 in the depth direction, the bulk density of the chopped chips 110 is preferably 0.04 g / cc or more and 0.16 g / cc or less, more preferably 0.06 g / cc or more and 0.14 g / cc or less, and even more preferably 0.08 g / cc or more and 0.12 g / cc or less.

[0025] As long as the above conditions are met, there is no particular limitation on the shape of chopped chips 110. For example, chopped chips 110 may have a shape with an odd number of bent portions 116e, 116f, and 116g as shown in Fig. 3A, or may have two bent portions 116h and 116i as shown in Fig. 3B.

[0026] As shown in FIGS. 2, 3A, and 3B, chopped chips 110 preferably have a shape in which linear portions 112a and 112b, each having a predetermined length, are connected by a shorter connecting portion 112c disposed therebetween. The linear portions 112a and 112b, each having a predetermined length, can increase the strength of the random sheet, and the connecting portion 112c changes the orientation direction of the reinforcing fibers 112 for each linear portion, thereby making the orientation direction of the reinforcing fibers 112 within the random sheet more random and orienting more reinforcing fibers 112 in the depth direction. The connecting portion 112c may be shorter than the linear portions 112a and 112b and may be linear, bent multiple times, or twisted. The lengths of the linear portions 112a and 112b are not particularly limited, but are preferably 0.5 mm to 10 mm, more preferably 1 mm to 8 mm, and even more preferably 2 mm to 6 mm. The lengths of the straight portions 112a and 112b may also be calculated as the average of the measured values ​​for 100 randomly selected chopped chips 110.

[0027] It is preferable that the reinforcing fibers 112 are arranged parallel to one another throughout the entire chopped chips 110. When the chopped chips 110 have the above-described straight portions 112a, 112b, and connecting portions 112c, it is preferable that the reinforcing fibers 112 are arranged parallel to one another at least in the straight portions 112a and 112b. It is also preferable that the reinforcing fibers 112 are arranged parallel to one another in the connecting portions 112c, but this does not apply when the reinforcing fibers 112 are bent or twisted in multiple ways.

[0028] The chopped chips 110 may also be branched.

[0029] 1-1-1―2. Chip materials The material of the chopped chips 110 is not particularly limited, and may be any material that can be used in the manufacture of fiber reinforced resin.

[0030] The material of the reinforcing fibers 112 is not particularly limited. For example, carbon fiber, glass fiber, aramid fiber, alumina fiber, silicon carbide fiber, boron fiber, metal fiber, etc. can be used as the reinforcing fibers. Of these, carbon fiber and glass fiber are preferred, and carbon fiber is more preferred. The materials of the reinforcing fibers 112 (including whether or not they are subjected to a sizing treatment, which will be described later) may be different from each other, but are preferably the same from the viewpoint of further increasing the flexural modulus of the random sheet to be manufactured.

[0031] From the viewpoint of sufficiently enhancing the effect of improving strength by the reinforcing fibers, the reinforcing fibers 112 preferably have an average diameter of 1 μm or more and 20 μm or less, and more preferably 4 μm or more and 10 μm or less.

[0032] The reinforcing fibers 112 may also be subjected to a sizing treatment using a sizing agent.

[0033] The sizing agent is not particularly limited, but is preferably a modified polyolefin, more preferably a modified polyolefin containing a metal carboxylate. The modified polyolefin is, for example, an unmodified polyolefin in which a carboxylic acid group, a carboxylic anhydride group, or a carboxylic ester group is grafted onto the polymer chain of the unmodified polyolefin, and a salt is formed between the functional group and a metal cation.

[0034] The unmodified polyolefin is preferably an ethylene polymer containing 50 mol% or more of structural units derived from ethylene, or a propylene polymer containing 50 mol% or more of structural units derived from propylene. Examples of the ethylene polymer include ethylene homopolymers and copolymers of ethylene and an α-olefin having from 3 to 10 carbon atoms. Examples of the propylene polymer include propylene homopolymers and copolymers of propylene and ethylene or an α-olefin having from 4 to 10 carbon atoms. The unmodified polyolefin is preferably homopolypropylene, homopolyethylene, ethylene-propylene copolymer, propylene-1-butene copolymer, or ethylene-propylene-1-butene copolymer.

[0035] The content of the above-mentioned reinforcing fibers relative to the total mass of the chopped chips 110 is preferably 20% by mass or more and 80% by mass or less, more preferably 30% by mass or more and 75% by mass or less, even more preferably 30% by mass or more and 65% by mass or less, and particularly preferably 35% by mass or more and 60% by mass or less.

[0036] The content of the above-mentioned reinforcing fibers relative to the total volume of the chopped chips 110 is preferably 10% by volume or more and 70% by volume or less, more preferably 15% by volume or more and 60% by volume or less, and even more preferably 20% by volume or more and 60% by volume or less.

[0037] The material of the matrix resin 114 is not particularly limited, and the matrix resin 114 may be a thermoplastic resin, a thermosetting resin, or a crystalline resin.

[0038] Examples of the thermoplastic resin include polyolefin resins such as polyethylene, polypropylene, polybutene, and poly4-methyl-1-pentene, polyamide resins, polyester resins, polystyrene resins, thermoplastic polyimide resins, polyamideimide resins, polycarbonate resins, polyphenylene ether resins, polyphenylene sulfide resins, polyacetal resins, acrylic resins, polyetherimide resins, polysulfone resins, polyether ketone resins, polyether ether ketone resins, polyarylate resins, polyether nitrile resins, vinyl chloride resins, ABS resins, and fluororesins.

[0039] Examples of the thermosetting resin include epoxy resin, phenol resin, melamine resin, urea resin, diallyl phthalate resin, silicone resin, urethane resin, furan resin, ketone resin, xylene resin, thermosetting polyimide resin, unsaturated polyester resin, and diallyl terephthalate resin.

[0040] Among these, thermoplastic resins are preferred from the viewpoint of further improving the moldability of the random sheet to be produced. Among the thermoplastic resins, polyamide resins and polyolefin resins are preferred, with polyolefin resins being more preferred from the viewpoint of enabling molding at lower temperatures and further improving production efficiency, and polypropylene being even more preferred from the viewpoints of light weight, high rigidity, low water absorption, and further improved chemical resistance and chemical stability. The materials of the matrix resin 114 (including additives and other components described below) may be different from each other, but are preferably the same from the viewpoint of further increasing the flexural modulus of the random sheet to be produced.

[0041] The matrix resin 114 may be a resin composition containing additives, such as known fillers (inorganic fillers and organic fillers), pigments, dyes, weather-resistant stabilizers, heat-resistant stabilizers, antistatic agents, antislip agents, antioxidants, antifungal agents, antibacterial agents, flame retardants, and softeners.

[0042] Furthermore, the matrix resin 114 may contain other components such as resins other than those mentioned above, or short fibers having a length shorter than the reinforcing fibers mentioned above.

[0043] The content of matrix resin 114 relative to the total mass of chopped chips 110 is preferably 20% by mass or more and 80% by mass or less, more preferably 25% by mass or more and 70% by mass or less, even more preferably 35% by mass or more and 70% by mass or less, and particularly preferably 40% by mass or more and 65% by mass or less.

[0044] 1-1-1―3. Chip manufacturing Chopped chips 110 can be manufactured by cutting a fiber-reinforced resin sheet (hereinafter simply referred to as a "Uni-Direction (UD) sheet") made of a plurality of unbent reinforcing fibers oriented in one direction and impregnated with a matrix resin.

[0045] 1-1-1―3-1.Preparing the UD sheet The UD sheet can be produced by a known method in which reinforcing fibers aligned in one direction are impregnated with a resin that will serve as the matrix resin material.

[0046] 1-1-1―3-2.Cutting the UD sheet The UD sheet can be cut using a known cutter. At this time, the UD sheet is first folded so that the fold lines are perpendicular to the reinforcing fibers, and the folded UD sheet is then cut so that the aspect ratio falls within the above range, thereby obtaining chopped chips 110.

[0047] Alternatively, the chopped chips 110 can be obtained by passing the UD sheet between a pair of rollers, each of which has a plurality of grooves, arranged so that the grooves intermesh with each other.

[0048] 4 is a schematic diagram showing how a UD sheet is passed through the roller pair to produce chopped chips 110. The roller pair 400 comprises a roller 410a on which multiple cutter discs 412a are coaxially arranged, and a roller 410b on which multiple cutter discs 412b are similarly coaxially arranged, with the cutter discs being arranged to fit together.

[0049] A UD sheet 420, which is made of a plurality of unbent reinforcing fibers 422 oriented in one direction and impregnated with a matrix resin 424, is passed between rollers 410a and 410b. This causes each cutter disc to cut the UD sheet 420 in the direction of its passage (a direction perpendicular to the coaxial arrangement direction of the cutter discs). Each cutter disc is provided with horizontal cutting blades 414a and 414b on its surface, which also cut the UD sheet 420 in the direction perpendicular to the direction of its passage.

[0050] At this time, the UD sheet is passed so that the angle between the orientation direction of the reinforcing fibers of the UD sheet and the passing direction is between 60° and 90°. As a result, the portions of the UD sheet 420 that contacted the cutter discs 412a and 412b are not partially cut, but remain uncut at a predetermined length, becoming the above-mentioned straight portions 112a and 112b. The portions between these that did not contact the cutter discs are subjected to greater stress and deform, becoming the above-mentioned connecting portion 112c.

[0051] Furthermore, the UD sheet 420 is also cut by the side cutting blades 414a and 414b in a direction parallel to the reinforcing fibers 422. At this time, a strong stress is applied to the UD sheet 420 in the direction of passing between the rollers, and a force is also applied to tear the UD sheet 420 in a direction parallel to the orientation direction of the reinforcing fibers 422. In this way, the UD sheet is cut into chopped chips having an elongated shape with a large aspect ratio (L / W) and having bent portions.

[0052] 1-1-2.Paving In this step, the chopped chips 110 are spread out flatly. For example, the chopped chips 110 may be spread out tightly inside a mold for press molding.

[0053] In this step, the chopped chips 110 are randomly scattered inside the mold without gaps. At this time, it is preferable to lay the chopped chips 110 so that they overlap and form multiple layers to prevent gaps from forming. Furthermore, it is preferable to lay the chopped chips 110 so that the orientation of the reinforcing fibers in each chopped chip 110 is random (the orientation in the length direction of the chopped chips 110). For example, the orientation of the chopped chips 110 may be adjusted manually, or chopped chips 110 that have been pre-oriented unevenly may be scattered inside the mold. Specifically, the orientation of the chopped chips 110 can be made random by shaking the chopped chips 110, using a rotary valve, or laying the chopped chips 110 using a belt feeder or vibrating feeder.

[0054] The planar shape and thickness of the spread chopped chips 110 may be determined in accordance with the shape of the random sheet to be formed.

[0055] 1-2. Integration step (step S120) Next, the spread chopped chips 110 are heated and pressurized to integrate the chopped chips 110. This results in a random sheet in which the reinforcing fibers are randomly oriented.

[0056] The press-molding mold and the mold facing the mold are heated and pressed against each other to integrate the chopped chips 110 packed inside the mold. If the matrix resin is a thermoplastic resin, the heating temperature may be any temperature at which the thermoplastic resin melts, and may be equal to or higher than the melting point of the matrix resin but not higher than 50°C above the melting point. If the matrix resin is a thermosetting resin, the heating temperature may be any temperature at which the thermosetting resin hardens, and may be any temperature at which the thermosetting resin hardens but not higher than the hardening temperature of the matrix resin but not higher than 50°C above the hardening temperature. The pressure applied during the compression bonding may be 0.5 MPa or higher and 5 MPa or lower. However, the heating and pressurizing method is not limited to press molding using a press molding machine. Other methods of heating and pressurizing include press molding using a double-belt press and autoclave molding using an autoclave.

[0057] Thereafter, the sheet is sufficiently cooled and then removed to obtain a random sheet.

[0058] 2. Random Sheet The random sheet produced by the above-described method is made up of reinforcing fibers having bent portions randomly dispersed inside a matrix resin.

[0059] The thickness of the random sheet is preferably 0.5 mm or more and 10.0 mm or less, and more preferably 1.0 mm or more and 5.0 mm or less. If the thickness is 0.5 mm or more, it is possible to suppress the occurrence of unintended holes due to gaps that occur when the chopped chips 110 are laid out or the movement of the chopped chips 110 when pressed. On the other hand, if the thickness is 10.0 mm or less, it is possible to make the properties of the random sheet 500 more uniform.

[0060] In the random sheet of this embodiment, the standard deviation of the fiber orientation distribution within the sheet is preferably 30 or more. Specifically, the inside of a 3 mm long × 3 mm wide test piece cut out from the random sheet is X-ray imaged, and the carbon fiber orientation coefficient in the Z direction is calculated from image data in the XY direction (length-width direction) plane and image data in the Z direction (thickness direction) plane. The Z direction orientation coefficient is calculated five times at different positions, and the standard deviation of the fiber orientation distribution in the Z direction (thickness direction) of each random sheet is calculated from these results.

[0061] The larger the standard deviation, the greater the distribution of the degree of orientation of the reinforcing fibers in the thickness direction at each site in the random sheet, that is, the more randomly the reinforcing fibers are oriented.

[0062] The random sheet in this embodiment may be laminated with a resin film. The resin film may be, for example, a protective film for covering the reinforcing fibers protruding from the matrix resin to smooth the surface of the random sheet. This resin film may contain additives, such as weather stabilizers and flame retardants, for suppressing changes in the properties of the random sheet. The resin material constituting the resin film is not particularly limited, and any resin may be used. Furthermore, a resin film with a higher hardness for suppressing scratches on the random sheet may be arranged on the outside of multiple resin films with a lower hardness for covering the protruding reinforcing fibers. Furthermore, the resin film may be visible light transparent so as not to impair the design of the random sheet.

[0063] [Application] The random sheet is not limited to any particular application, but is extremely useful for applications requiring light weight and relatively high strength, such as electrical components, PC housings, mobile phone covers, automobile parts, motorcycle parts, furniture, partitions, screen walls, doors, sliding doors, etc. It is also extremely useful for applications requiring design, such as building materials, wallpaper, flooring materials, decorative boards, etc. [Example]

[0064] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to the descriptions in the examples.

[0065] 1. Creating a random sheet 1-1. Preparation of Random Sheet 1 (Example 1) Chopped chips were produced using a UD sheet (manufactured by Mitsui Chemicals, Inc., TAFNEX ("TAFNEX" is a registered trademark of the company)) in the following manner. This UD sheet contained polypropylene and carbon fiber, and had a fiber volume fraction (Vf) of 50% by volume and a thickness of 160 μm.

[0066] The UD sheet was fed into a cross-cut shredder (Paper & CD Shredder 400-PSD010, manufactured by Saiwa Supply Co., Ltd.) so that the orientation direction of the carbon fiber was perpendicular to the direction of insertion into the shredder, to obtain chopped chips 1. Chopped chips 1 was poured into a 2000 ml cup (Disposable Cup (2000 ml) manufactured by AS ONE Corporation) up to the 2000 ml mark, and the weight was measured. The bulk density calculated assuming a volume of 2000 ml was 0.1 g / cc.

[0067] One hundred chopped chips 1 were randomly sampled, and their length (L), width (W), thickness, and the number of bent portions of the chopped chips and carbon fibers were measured. The average values ​​were 12 mm for length (L), 3 mm for width (W), and 160 μm for thickness, with four bent portions. The aspect ratio (L / W) was 4. Chopped chips 1 had a shape in which straight portions with an average length of 3.1 mm were connected by shorter connecting portions. Chopped chips 1 also had a curvature of 0.72, which is the ratio of the length (L) to the maximum length (EL) of the reinforcing fibers contained in the chip.

[0068] 270 g of chopped chips 1 were placed in a plastic bag, inflated with air, and shaken for 5 minutes. The bag was then spread flat in a 300 mm x 300 mm mold. The mold containing the chopped chips was heated to 180 °C and pressurized to 2 MPa (gauge pressure 10 MPa, cylinder diameter 180 mm, spacer size 350 mm) using a vacuum forming machine (Kansai Roll Co., Ltd., 294 kN, 400 x 400, two-stage heating and cooling vacuum forming machine) while vacuum degassing. Random sheet 1 measuring 300 mm long, 300 mm wide, and 2.24 mm thick was obtained.

[0069] 1-2. Preparation of Random Sheet 2 (Comparative Example 1) The UD sheet was cut with a strand cutter to obtain chopped chips 2. The bulk density of chopped chips 2, determined by the above method, was 0.40 g / cc.

[0070] One hundred chopped chips 2 were randomly sampled, and the length (L), width (W), thickness, number of bent portions of the chopped chips and carbon fiber, and curvature were measured. The average values ​​for each were 3 mm for length (L), 1 mm for width (W), and 160 μm for thickness, and the number of bent portions was 0. The aspect ratio (L / W) was 3. The curvature was 1.00.

[0071] A random sheet 3 having a length of 300 mm, a width of 300 mm and a thickness of 1.85 mm was obtained in the same manner as in the molding of random sheet 1, except that the same amount of chopped chips 2 was used instead of chopped chips 1.

[0072] 1-3. Preparation of Random Sheet 3 (Comparative Example 2) The UD sheet was fed into a cross-cutting shredder (Paper & CD Shredder 400-PSD010, manufactured by Saiwa Supply Co., Ltd.) so that the orientation direction of the carbon fibers was at 45° to the insertion direction into the shredder, to obtain chopped chips 3. The bulk density of chopped chips 3, determined by the above method, was 0.05 g / cc.

[0073] One hundred chopped chips 3 were randomly sampled, and their length (L), width (W), thickness, number of bent portions of the chopped chips and carbon fiber, and curvature were measured. The average values ​​were 45 mm for length (L), 3 mm for width (W), and 160 μm for thickness, with 12 bent portions. The aspect ratio (L / W) was 15. The curvature was 0.95. Chopped chips 3 also had a twisted, spiral shape, with straight portions averaging 4.3 mm in length connected by shorter connecting portions.

[0074] A random sheet 3 measuring 300 mm in length, 300 mm in width and 1.93 mm in thickness was obtained in the same manner as in the random sheet 1, except that the same amount of chopped chips 3 was used instead of chopped chips 1.

[0075] 1-4. Preparation of Random Sheet 4 (Comparative Example 3) The UD sheet was cut into a tape shape with a width of 12.5 mm in a direction parallel to the orientation direction of the carbon fibers. This tape-like UD sheet was cut into a length of 15 mm using a guillotine cutter to obtain chopped chips 4. The bulk density of chopped chips 4, determined by the above method, was 0.21 g / cc. The length (L) of these chopped chips 4 was 15 mm, the width (W) was 12.5 mm, the thickness was 160 μm, and the number of bends was 0. The aspect ratio (L / W) was 1.2. The curvature was 1.00.

[0076] A random sheet 4 having a length of 300 mm, a width of 300 mm and a thickness of 1.86 mm was obtained in the same manner as in the molding of random sheet 1, except that the same amount of chopped chips 4 was used instead of chopped chips 1.

[0077] 2. Measurement and Evaluation 2-1. Bending test Test pieces measuring 15 mm in width and 100 mm in length were cut from each random sheet. A bending test was performed in accordance with JIS K 7074 (1988) using a bending tester (Shimadzu Corporation's Autograph AG-Xplus equipped with a 5 kN load cell and a plastic three-point bending test jig).

[0078] In accordance with the method specified in JIS K 7171 (2016), a bending test was conducted at a test speed of 1 mm / min, a support distance of 48 mm, and a test temperature of 23°C to measure the bending stress and bending modulus. Measurements were conducted on five test pieces, and the average values ​​were calculated to determine the bending stress and bending modulus of each random sheet.

[0079] 2-2. Fiber orientation distribution A 3mm long x 3mm wide measurement piece was cut from the random sheet. Using an X-ray CT scanner (Rigaku Corporation, nano 3DX), the state of the carbon fibers inside the measurement piece was measured and imaged under the following conditions: Cu target, 1080° lens, binning 1, 1000 scanning angles, 12 seconds of integration time at each angle, pixel resolution of 1,300 μm / pixel, and 16-bit measurement data. Using VGSTUDIO MAX (Volume Graphics Inc.), the carbon fiber orientation coefficient in the Z direction was calculated from image data of one XY (length-width) plane and one Z (thickness) plane. Five calculations of the Z direction orientation coefficient were performed at different positions, and the standard deviation of the fiber orientation distribution in the Z direction (thickness direction) of each random sheet was calculated from these results.

[0080] 3.Results Table 1 shows the manufacturing conditions and evaluation results of the random sheets 1 to 4 obtained above.

[0081] [Table 1]

[0082] As can be seen from Table 1, random sheets produced using chopped chips having an aspect ratio (L / W) of 2 or more and 10 or less and having one to eight bends had higher bending stress and bending modulus. [Industrial Applicability]

[0083] The random sheet of the present invention has a higher bending stress and bending modulus than conventional random sheets. Therefore, the present invention is expected to open up the possibility of using random sheets in a wider range of applications and contribute to the development of various fields related to random sheets. [Explanation of symbols]

[0084] 110 Chopped Chips 112 Reinforced Fiber 112a, 112b Straight section 112c connection part 114 Matrix Resin 116a, 116b, 116c, 116d, 116e, 116f, 116g, 116h, 116i Bending part 400 Roller vs. 410a, 410b rollers 412a, 412b Cutter disc 414a, 414b side blade 420 UD seat 422 Reinforced Fiber 424 Matrix Resin

Claims

1. A step of laying fiber-reinforced resin chips in a flat surface; and applying heat and pressure to the spread chips to integrate the chips together. The chip has an aspect ratio (L / W) of 2 to 10, which is the ratio of length (L) to width (W), The chip is formed by impregnating a plurality of reinforcing fibers oriented in the same direction with a matrix resin, and has one to eight bent portions where the shape of the chip and the reinforcing fibers are bent. Manufacturing method of random sheet.

2. The method for manufacturing a random sheet according to claim 1 , wherein the chip has a shape in which linear portions having a predetermined length are connected by shorter connecting portions.

3. The method for manufacturing a random sheet according to claim 1 or 2, wherein the chips have a width (W) of 5 mm or less.

4. The chip includes a step of preparing a fiber reinforced resin sheet in which a matrix resin is impregnated into a plurality of unbent reinforced fibers oriented in one direction; A step of forming the chip having the bent portion by passing the fiber reinforced resin sheet between a pair of rollers, each of which has a plurality of cutter discs, arranged so that the cutter discs fit together; The chip is manufactured by a method for manufacturing the chip having the following: The method for producing the random sheet according to any one of claims 1 to 3.

5. The method for producing a random sheet according to any one of claims 1 to 4, wherein the matrix resin includes a thermoplastic resin.

6. The method for producing a random sheet according to any one of claims 1 to 5, wherein the matrix resin contains polypropylene.

7. The method for manufacturing a random sheet according to any one of claims 1 to 6, wherein the chip has a curvature (L / EL), which is the ratio of the length (L) to the length (EL) of the extended chip, of 0.50 to 0.

90.

8. A random sheet in which a plurality of chips are laid out on a plane and integrated by heating and pressurizing, The chip has an aspect ratio (L / W) of 2 to 10, which is the ratio of length (L) to width (W), The chip is a random sheet made of a plurality of reinforcing fibers arranged and oriented in the same direction and impregnated with a matrix resin, and having one to eight bends.

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