Method for producing thermoplastic prepreg

Abstract

To provide a method for producing prepreg that is of high quality and also allows for higher production speeds.SOLUTION: There is provided a method for producing a single prepreg from a single strand of reinforcing fiber roving by passing the reinforcing fiber roving through the inside of a die supplied with a thermoplastic resin in a horizontal or slanted direction, and applying the thermoplastic resin to the reinforcing fiber roving. The die has multiple impregnating bars in a direction perpendicular to the reinforcing fiber roving, and the thermoplastic resin is impregnated into the reinforcing fiber roving by making the reinforcing fiber roving come into contact with the impregnating bars, and the method for producing a prepreg satisfies the following conditions (a) to (c): (a) A radius r of the impregnating bar in contact with the reinforcing fiber roving is 5 mm or more and 30 mm or less. (b) An included angle formed by the contact between the impregnating bar and the reinforcing fiber roving is 10° or more and 80° or less per one impregnating bar. (c) A total of the included angles formed by multiple impregnating bars is between 50° or more and 500° or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing a thermoplastic prepreg by uniformly impregnating a reinforcing fiber roving with a thermoplastic resin. [Background technology]

[0002] Fiber-reinforced composite materials (FRP), which are made by impregnating continuous reinforcing fibers with matrix resins including thermoplastic resins and thermosetting resins, have excellent specific strength and specific stiffness, and are highly effective in reducing weight, so they are used in a variety of fields, including aerospace materials, automotive materials, industrial materials, pressure vessels, building materials, housings, medical applications, and sports applications. Carbon fiber-reinforced composite materials (CFRP) are widely and preferably used when high mechanical properties and light weight are required. On the other hand, glass fiber-reinforced composite materials (GFRP) may be used when cost is prioritized over mechanical properties and light weight. FRP is manufactured by impregnating reinforcing fiber bundles with matrix resin to obtain an intermediate substrate (prepreg), which is then laminated and molded, and when a thermosetting resin is used, it is heat-cured to produce FRP components.

[0003] Currently, thermosetting CFRP is mainly used for aircraft applications, but it takes a long time to mold, making it difficult to produce a large number of parts in a short time. Therefore, thermoplastic CFRP, which can be molded at high speed without causing chemical changes in the resin during molding, has attracted attention, and research and development is being carried out in various countries. In addition, while thermosetting CFRP needs to be stored in a low-temperature environment such as a freezer, thermoplastic CFRP can be stored at room temperature, which is also advantageous in terms of management costs.

[0004] One example of a method for producing prepregs has been proposed in Patent Document 1. This method applies matrix resin to a reinforcing fiber sheet by passing the sheet through an application section in which matrix resin is stored, and the application section has a section in which the cross-sectional area continuously decreases along the running direction of the fiber sheet, thereby increasing the pressure of the matrix resin and impregnating the interior of the fiber bundle with the matrix resin.

[0005] As a method for producing a prepreg using a thermoplastic resin, a horizontal drawing method (Patent Document 2) is known in which a reinforcing fiber bundle is conveyed horizontally and passed through a die to impregnate the reinforcing fiber bundle with a thermoplastic resin. Patent Document 2 describes that a plurality of reinforcing fiber bundles are separately introduced into a die filled with molten thermoplastic resin, and are opened, impregnated and laminated by a fixed guide, and finally drawn out from the die as a single sheet-like prepreg.

[0006] In recent years, efforts have been made to mechanize and automate the lamination of sheet-shaped prepregs in order to improve the production efficiency of components made of thermoplastic CFRP, and narrow tape-shaped prepregs are preferably used for this purpose. Narrow tape-shaped prepregs can be obtained by slitting wide sheet-shaped prepregs to the desired width or by directly impregnating narrow reinforcing fiber rovings with thermoplastic resin.

[0007] As a method for slitting a wide-width sheet-like prepreg into a narrow-width tape, for example, there has been a proposal as shown in Patent Document 1. This is a method for simultaneously slitting wide-width and narrow-width prepreg tapes, and is a method for slitting tapes of multiple widths from the same master roll. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication WO2020 / 031766 Brochure [Patent Document 2] International Publication WO2012 / 002417 Brochure [Patent Document 3] Special Publication No. 2015-519210 Summary of the Invention [Problem to be solved by the invention]

[0009] In the method of Patent Document 1, resin impregnation is achieved by increasing the resin pressure in the application area, but in matrix formulations with high resin viscosity, such as thermoplastic resins, impregnation becomes insufficient, resulting in a deterioration of the mechanical properties of the thermoplastic CFRP.

[0010] In addition, in the method of Patent Document 2, fiber bundles containing a large amount of thermoplastic resin are bundled and pulled out, so a large amount of resin is squeezed out at the nozzle. Continuous running at high speed generates fuzz, so production can only be performed at a very slow speed, which is a problem in terms of low productivity.

[0011] On the other hand, in the slitting of sheet-like prepregs as shown in Patent Document 3, if there are area weight variations in the width direction of a wide-width sheet-like prepreg, area weight variations will also occur in each narrow-width prepreg when slit, and this area weight variation becomes more noticeable as the slit width becomes narrower.

[0012] Thus, a method for efficiently producing a high-quality narrow prepreg has not yet been established. The object of the present invention is to provide a method for producing a narrow thermoplastic prepreg that has little unevenness in the basis weight of each yarn and can sufficiently impregnate the inside of the fiber bundle with thermoplastic to produce a high-quality prepreg and can increase the production speed. [Means for solving the problem]

[0013] In order to achieve the above object, the present invention mainly has the following configuration. [1] A method for producing one prepreg from one reinforcing fiber roving by passing a reinforcing fiber roving horizontally or obliquely through a die to which a thermoplastic resin has been supplied, thereby imparting the thermoplastic resin to the reinforcing fiber roving, wherein the die is provided with a plurality of impregnation bars arranged in a direction perpendicular to the reinforcing fiber roving, and the reinforcing fiber roving is impregnated with the thermoplastic resin by contacting the reinforcing fiber roving with the impregnation bars, and the method for producing a prepreg satisfies the following conditions (a) to (c): (a) The radius r of the part of the impregnated bar that comes into contact with the reinforcing fiber roving is 5 mm or more and 30 mm or less. (b) The included angle formed by the contact between the impregnated bar and the reinforcing fiber roving is 10° or more and 80° or less per impregnated bar. (c) The total included angle of multiple impregnated bars is 50° or more and 500° or less [2] The method for producing a prepreg described in [1], wherein the die is provided with a liquid reservoir portion whose cross-sectional area continuously decreases along the running direction of the reinforcing fiber roving impregnated with a thermoplastic resin, and a narrowed portion having a slit-shaped cross-section connected to the liquid reservoir portion, and the tension T of the primary prepreg immediately after being pulled out of the die is 0.3% or more and 7% or less of the tensile strength (N) of one reinforcing fiber roving. [3] The method for producing a prepreg according to [1] or [2], wherein the void ratio of the primary prepreg immediately after being pulled out from the narrowed portion of the die is 0.1% or more and 15% or less. [4] The method for producing a prepreg according to [1], wherein the thermoplastic resin has a viscosity of 1 to 500 Pa s at a melting point (Tm) + 50°C at a shear rate of 1,216 sec-1. [5] The method for producing a prepreg according to [1], wherein the total contact length between the reinforcing fiber roving and the multiple impregnated bars is 5 mm or more and 250 mm or less. [6] The method for producing a prepreg according to [2], wherein the length H of the portion where the cross-sectional area of ​​the liquid pool continuously decreases is 5 mm or more and 30 mm or less, and the tapered opening angle θ is 20° or more and 90° or less. [7] The method for producing a prepreg according to [1], wherein at least one of the plurality of impregnated bars has a groove for regulating the width of the reinforcing fiber roving. [8] The method for producing a prepreg according to [7], wherein the width L of the narrowed portion of the die and the restricted width W of the impregnated bar that finally comes into contact with the reinforcing fiber roving inside the die satisfy the following formula (1). L×0.7≦W≦L×1.3(1) [9] A method for producing a prepreg according to [1], comprising the step of re-impregnating the primary prepreg pulled out from the nozzle of the die.

[10] The method for producing a prepreg according to [9], wherein the void ratio of the prepreg after the additional impregnation is less than 2%.

[11] The method for producing a prepreg according to [9], further comprising a step of shaping the prepreg after the additional impregnation. Effect of the Invention

[0014] According to the method for producing a thermoplastic prepreg of the present invention, clogging due to fluff can be significantly suppressed and prevented. Furthermore, it is possible to run the reinforcing fiber roving continuously and at high speed, thereby improving the productivity of the thermoplastic prepreg. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a method and an apparatus for producing a thermoplastic prepreg according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a diagram showing examples of shapes of an impregnation bar. [Diagram 3] FIG. 1 is a diagram showing the included angle and contact length due to contact between an impregnated bar and a reinforcing fiber roving. [Figure 4] FIG. 1 is an isometric view of an impregnation bar having width-constraining grooves. [Diagram 5] FIG. 2 is an enlarged view of a resin reservoir portion and a narrowed portion. [Figure 6] FIG. 2 is a diagram showing an impregnation bar, a resin reservoir, and a reinforcing fiber roving passing through a narrowed portion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] A preferred embodiment of the present invention will be described with reference to the drawings. Note that the following description is merely an example of an embodiment of the present invention, and the present invention should not be construed as being limited thereto, and various modifications are possible without departing from the scope of the present invention.

[0017] <Outline of prepreg manufacturing method> First, the outline of the method for producing a thermoplastic prepreg of the present invention will be described with reference to Fig. 1. Fig. 1 is a schematic cross-sectional view showing the method and apparatus for producing a thermoplastic prepreg according to an embodiment of the present invention.

[0018] The reinforcing fiber roving 1a is drawn from the creel 11, passes through the direction-changing roll 12, and is introduced obliquely downward into a die consisting of a lower die 24 and an upper die 25. An extruder 4 is connected to the die, and the thermoplastic resin 2a introduced from a hopper 3 is melted and kneaded using the extruder 4, and is supplied in a fixed amount into the die through a gear pump 5. The die is provided with a plurality of impregnation bars having arc-shaped surfaces, and the semicircular outer surfaces are arranged so that they face alternately in the up and down directions. It is preferable to introduce the reinforcing fiber roving obliquely downward into the inside of the die, because it is possible to fill the inside of the die with the molten resin 2b and to make the impregnation bars completely immersed in the molten resin. Specifically, it is preferable that the height of the apex C of the lower die 24 is higher than the height of the bottom surface B of the upper die 25. In addition, the outlet side of the die is provided with a liquid pool 22 whose cross-sectional area continuously decreases along the running direction of the reinforcing fiber roving, and a narrowed portion 23 with a slit-shaped cross section that communicates with the liquid pool. The base material 1b pulled out from the die is cooled and solidified by a cooling roll 13 to become a primary prepreg 1c. A take-up machine 14 is provided as a running mechanism for transporting the reinforcing fiber roving or the thermoplastic prepreg in the manufacturing method for thermoplastic prepreg of the present invention. Also, a winding machine 15 is provided for winding up the manufactured thermoplastic prepreg.

[0019] <Reinforced fiber roving> Here, examples of the reinforcing fiber roving include carbon fiber, glass fiber, metal fiber, metal oxide fiber, metal nitride fiber, and organic fiber (aramid fiber, polybenzoxazole fiber, polyvinyl alcohol fiber, polyethylene fiber, polyester fiber, polyamide fiber, etc.), but it is preferable to use carbon fiber from the viewpoint of the mechanical properties and light weight of FRP. The total number of filaments (single fibers) of the reinforcing fiber is preferably 1,000 to 50,000. More preferably, it is 3,000 to 30,000. The upper limit of the total number of filaments of the reinforcing fiber may be any number that can maintain a good balance between the quality such as voids and dispersibility and the handleability. One reinforcing fiber roving is preferably composed of 1,000 to 50,000 single fibers having an average diameter of 5 to 10 μm. It is preferable that the creel is provided with a tension control mechanism when the reinforcing fiber roving is drawn out. As the tension control mechanism, a known one can be used, but examples include a brake mechanism. The tension can also be controlled by adjusting the yarn guide.

[0020] In addition, as the sizing agent to be applied to the reinforcing fiber roving, it is preferable to use one having a heat loss of 5% or less at 300°C. More preferably, it is one having a heat loss of 15% or less at 350°C. When a sizing agent that is difficult to thermally decompose is used, fluff is unlikely to occur in the resin impregnation process, and gas generation in the die can be minimized, so that the effects of the present invention can be maximized. This effect is particularly remarkable in heat-resistant thermoplastic resins (e.g., polyphenylene sulfide, polyether ether ketone, polyether ketone ketone, polyether imide, aromatic polyamide, etc.) whose processing temperature exceeds about 300°C. When carbon fibers to which a sizing agent is not applied are used, there is an advantage that gas generation is almost eliminated, but fluff generation is significant, and not only is it impossible to obtain a high-quality thermoplastic prepreg, but it may also be difficult to achieve high productivity. The above-mentioned heat loss refers to the ratio of weight loss of the sizing agent at 300°C and 350°C when heated from 25°C to 400°C at a heating rate of 10°C / min in an air atmosphere in a TG (thermogravimetric) method.

[0021] The manufacturing method of the thermoplastic prepreg of the present invention is a method for manufacturing one prepreg from one continuous reinforcing fiber roving, but in order to increase productivity, it is preferable to run a plurality of reinforcing fiber rovings in parallel. In this case, it is preferable that each reinforcing fiber roving runs independently without contacting the other reinforcing fiber rovings. Specifically, it is preferable that there is a sufficient gap between each roving when passing through a direction changing roll, an impregnation bar, a liquid pool, a narrowed portion, and a take-off machine, or that the position of each reinforcing fiber roving is regulated by a groove or a jig so that the running position does not shift.

[0022] <Widening of reinforced fiber roving> In the present invention, it is also preferable to introduce the reinforcing fiber roving into the die after widening the reinforcing fiber roving from the viewpoint of improving impregnation and efficiently producing a thin prepreg. There is no particular limitation on the widening method, but examples include a method of mechanically applying vibration and a method of widening the reinforcing fiber roving by air flow. As a method of mechanically applying vibration, for example, as described in JP-A-2015-22799, there is a method of contacting the reinforcing fiber roving with a vibrating roll. As for the vibration direction, if the traveling direction of the reinforcing fiber roving is the X-axis, it is preferable to apply vibration in the Y-axis direction (horizontal direction) and Z-axis direction (vertical direction), and it is also preferable to use a combination of a horizontal vibrating roll and a vertical vibrating roll. In addition, it is preferable to provide a plurality of protrusions on the vibrating roll surface, since it is possible to suppress abrasion of the reinforcing fiber by the roll. As a method using an air flow, for example, the method described in Sen-i-gakkaishi, vol. 64, pp. 262-267 (2008) can be used.

[0023] <Preheating of reinforced fiber roving> In the present invention, it is preferable to heat the reinforcing fiber roving and then introduce it into the liquid pool, since this can suppress the temperature drop of the matrix resin and improve the viscosity uniformity of the matrix resin. It is preferable to heat the reinforcing fiber roving to a temperature close to the matrix resin temperature, and various means can be used as the heating means for this purpose, such as air heating, infrared heating, far-infrared heating, laser heating, contact heating, and heat medium heating (steam, etc.). Among these, infrared heating is preferable because the device is simple and the reinforcing fiber roving can be directly heated, so that it is possible to efficiently heat it to the desired temperature even if the running speed is high.

[0024] <Thermoplastic resin> The thermoplastic resin used in the present invention may be a polymer having a bond selected from carbon-carbon bonds, amide bonds, imide bonds, ester bonds, ether bonds, carbonate bonds, urethane bonds, urea bonds, thioether bonds, sulfone bonds, imidazole bonds, and carbonyl bonds in the main chain.Specific examples include polyacrylate, polyolefin, polyamide (PA), aramid, polyester, polycarbonate (PC), polyphenylene sulfide (PPS), polybenzimidazole (PBI), polyimide (PI), polyetherimide (PEI), polysulfone (PSU), polyethersulfone (PES), polyetherketone (PEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyaryletherketone (PAEK), and polyamideimide (PAI). In fields where heat resistance is required, such as aircraft applications, PPS, PES, PI, PEI, PSU, PEEK, PEKK, PEAK, etc. are suitable. On the other hand, in industrial applications and automotive applications, polyolefins such as polypropylene (PP), PA, polyester, PPS, etc. are suitable to increase molding efficiency. These may be polymers, or oligomers or monomers may be used for low viscosity and low temperature application. Of course, these may be copolymerized depending on the purpose, or various types may be mixed and used as polymer blends or polymer alloys.

[0025] <Viscosity of thermoplastic resin> It is preferable to select an optimum viscosity for the thermoplastic resin used in the present invention from the viewpoint of processability and stability. Specifically, it is preferable to set the viscosity of the thermoplastic resin at the melting point Tm+50°C in the range of 1 to 500 Pa s, since this can improve the impregnation of the thermoplastic resin into the reinforcing fiber roving, high-speed running property, and stable running property.

[0026] The viscosity was measured using a Toyo Seiki Co., Ltd. Capillograph 1C die with a hole length of 10.00 mm and a hole diameter of 0.50 mm. Approximately 20 g of sample was placed in a cylinder set to a temperature of the melting point Tm+50°C of the molten thermoplastic resin inside the die, and after holding for 5 minutes, the melt viscosity was measured at a shear rate of 1216 sec-1. The viscosity of the thermoplastic resin is more preferably 5 to 100 Pa s.

[0027] <Thermoplastic resin impregnation process> The thermoplastic resin impregnation process will be described with reference to the drawings. A plurality of reinforcing fiber rovings unwound from a creel 11 in FIG. 1 are introduced into a die in an obliquely downward direction by a direction-changing roll 12, and are brought into contact with an impregnation bar inside the die, thereby impregnating the reinforcing fiber rovings with a thermoplastic resin. This allows a primary prepreg 1c to be obtained. It goes without saying that the primary prepreg itself also corresponds to the prepreg of the present invention. Here, the horizontal direction is shown as the X direction in FIG. 1. In addition, in the present invention, the reinforcing fiber rovings can be passed in an inclined direction, and the inclined running and the horizontal running can be combined. The inclined direction refers to a direction intermediate between the horizontal direction and the vertical direction. More specifically, the horizontal direction or the inclined direction can be in the range of -80° to +80°, with the horizontal plane being 0°. It is described that the reinforcing fiber roving runs in an up-down diagonal direction when traveling between the impregnation bars inside the die, but in the liquid reservoir where the cross-sectional area continuously decreases and in the narrowed portion of the slit-shaped cross section connected to the liquid reservoir, the running direction of the reinforcing fiber roving is horizontal. The surface of the impregnation bar has a circular arc cross-sectional shape, and is installed in a manner that the circular arc cross-section continues in a direction perpendicular to the reinforcing fiber roving (Y direction in Figure 1). Although the same impregnation effect can be obtained even if the cross-sectional shape of the impregnation bar surface is elliptical, it is preferable that it is circular arc-shaped from the viewpoint of the processability of the impregnation bar. An example of the cross-sectional shape of the impregnation bar is shown in Figure 2. It is preferable that the part that contacts the reinforcing fiber roving is circular arc-shaped. However, it is preferable that the part that does not contact the reinforcing fiber roving is cut into a shape such as Figure 2 (b) or (c) from the viewpoint of miniaturization of the die.

[0028] FIG. 3 shows a cross-sectional state where the reinforcing fiber roving and the impregnation bar are in contact. In the present invention, the angle at which the arc-shaped surface of the impregnation bar and the reinforcing fiber roving are in contact is defined as the included angle, and the contact distance on the circumference is defined as the contact length. Even if the included angle is the same, the larger the radius r of the impregnation bar, the longer the contact length. The radius r of the part where the impregnation bar contacts the reinforcing fiber roving must be 5 mm or more and 30 mm or less. By making the radius r of the impregnation bar 5 mm or more and 30 mm or less, it is possible to achieve both impregnation performance and miniaturization of the die. More preferably, it is 10 mm or more and 20 mm or less. If the radius r of the impregnation bar is less than 5 mm, the number of impregnation bars required to sufficiently impregnate the reinforcing fiber roving with the thermoplastic resin increases, and the entire die becomes longer. On the other hand, if the radius r of the impregnation bar exceeds 30 mm, the size of the impregnation bar becomes too large, and the volume of the die becomes large. As the die becomes longer or its volume increases, the thermoplastic resin spends more time inside the die. This longer residence time accelerates the deterioration of the thermoplastic resin, raising concerns about increased gas generation and reduced physical properties of the prepreg.

[0029] The included angle formed by the contact between the impregnation bar and the reinforcing fiber roving must be 10° or more and 80° or less per impregnation bar. By having the included angle per impregnation bar be 10° or more and 80° or less, both the impregnation of the thermoplastic resin and the quality of the prepreg can be achieved. More preferably, it is 20° or more and 40° or less. If the included angle per bar is less than 10°, the number of impregnation bars required to sufficiently impregnate the reinforcing fiber roving with the thermoplastic resin increases, and the entire die becomes longer. On the other hand, if the included angle per bar exceeds 80°, the tension increase when passing through the impregnation bar becomes large, and the frequency of fuzz generation increases. In FIG. 1, the included angle per impregnation bar can be adjusted by changing the positions of the adjacent impregnation bars in the X and Z directions. The closer the X-direction distance between the adjacent impregnation bars, the larger the included angle per bar. In addition, the greater the Z-direction position of the arc surfaces of adjacent impregnated bars that face up and down alternately, the larger the included angle per bar can be. In this case, if the distance between adjacent impregnated bars is too close, the thermoplastic resin will not flow easily between the impregnated bars, and partial cavities may occur in the molten resin if the take-up speed is fast. If cavities occur, uneven impregnation will occur between the rovings running in parallel, so it is preferable that the X-direction distance between the impregnated bars is 3 mm or more. Similarly, it is preferable that the Z-direction distance between the arc surfaces of the impregnated bars and the bottom surface of the upper mold / bottom surface of the lower mold is 3 mm or more.

[0030] The total included angle when multiple impregnation bars are used must be 50° or more and 500° or less. By having the total included angle of multiple impregnation bars be 50° or more and 500° or less, it is possible to achieve both the impregnation of the thermoplastic resin and the production speed. More preferably, it is 150° or more and 400° or less. If the total included angle is less than 50°, the impregnation is insufficient and the void ratio in the prepreg becomes too high. On the other hand, if the total included angle exceeds 500°, the tension of the prepreg when pulled out from the die becomes too high, which increases the occurrence of fluff and the frequency of breakage of the prepreg.

[0031] Considering the relationship between the radius and the included angle of the impregnated bar described above, the total contact length between the reinforcing fiber roving and the multiple impregnated bars is preferably 5 mm or more and 250 mm or less, more preferably 30 mm or more and 100 mm or less.

[0032] <Width regulation of impregnated bar> It is widely known that the width of the reinforcing fiber roving is expanded when the reinforcing fiber roving is handled in molten resin in contact with an impregnation bar. The wider the reinforcing fiber roving is, the thinner the reinforcing fiber roving becomes, which is advantageous for impregnation. On the other hand, if the width at the time of entering the narrowed part is wider than the specified width of the narrowed part, the friction between both ends of the reinforcing fiber roving and the wall surface of the narrowed part increases, which may cause the generation of fluff or breakage. Therefore, in the present invention, it is preferable to provide a groove 21a for width regulation in the impregnation bar as shown in the isometric view of FIG. 4. In the present invention, it is also possible to combine multiple impregnation bars without width regulation and multiple impregnation bars with width regulation. It is also possible to arbitrarily change the regulation width for each impregnation bar when multiple impregnation bars are used. It is desirable that the width L of the narrowed part and the regulation width W of the impregnation bar that finally contacts the reinforcing fiber roving inside the die satisfy L×0.7≦W≦L×1.3. If it is within this range, it is possible to reduce the frequency of the above-mentioned generation of fluff and breakage. More preferably, the range is L x 0.9 ≤ W ≤ L x 1.1. In this case, it is important that the center positions of the width restrictions of all the impregnated bars in the Y direction in Figure 1 are aligned with the center position of the width of the narrowed portion.

[0033] Below, we will explain the combination of squeeze width restrictions when the width of the narrowed portion is 6 mm, the width of the reinforcing fiber roving before being introduced into the die is 8 mm, and the total number of impregnated bars is 6. However, the present invention is not limited to this, and various modifications are possible depending on the type of reinforcing fiber roving used and the width of the desired prepreg.

[0034] - Pass 5 impregnated bars with no width restriction, then pass 1 impregnated bar with a width of 6 mm. - Five 8mm wide impregnated bars are passed through, followed by one 6mm wide impregnated bar. - After passing two 8mm wide impregnated bars, two 7mm impregnated bars and two 6mm impregnated bars are passed in sequence.

[0035] <Thermoplastic prepreg weight quantification process> In the present invention, the reinforcing fiber roving impregnated with the thermoplastic resin has a liquid pool portion whose cross-sectional area decreases continuously along the running direction of the reinforcing fiber roving, and a narrowed portion having a slit-shaped cross-section that communicates with the liquid pool portion. FIG. 4 shows an enlarged view of the liquid pool portion and the narrowed portion. By passing through the liquid pool portion 22 and the narrowed portion 23, the excess thermoplastic resin contained in the reinforcing fiber roving is squeezed out, and a thermoplastic prepreg having a desired basis weight can be obtained. The basis weight can be adjusted by changing the height of the clearance J of the narrowed portion. When the reinforcing fiber roving impregnated with the resin by the impregnation bar passes through the portion 22 whose cross-sectional area decreases continuously in the running direction, the accompanying thermoplastic resin is gradually compressed, and the pressure of the thermoplastic resin increases as it moves toward the narrowed portion. When the resin pressure increases, the thermoplastic resin is more easily impregnated into the reinforcing fiber roving, which is based on the property (Darcy's law) that the degree of impregnation increases with the resin pressure when the resin is impregnated into a porous body. The increase in resin pressure increases as the tapered opening angle θ of the portion where the cross-sectional area of ​​FIG. 4 decreases continuously becomes acute, and increases as the taper length H of the portion increases. On the other hand, the higher the resin pressure in the liquid reservoir, the higher the tension of the prepreg pulled out of the die, and the more easily the alignment of the reinforcing fiber monofilaments is disturbed by the resin pressure, resulting in higher occurrence of fluff and higher frequency of breakage of the prepreg. In Patent Document 2, it is preferable to increase the impregnation effect by increasing the angle θ and increasing the angle H, but in the present invention, the thermoplastic resin is impregnated to the desired degree of impregnation when passing through the impregnation bar before passing through the liquid reservoir / narrowed portion, so that it is preferable from the viewpoint of productivity to reduce the resin pressure as much as possible when pulling out of the die. Specifically, it is preferable that the length H of the portion where the cross-sectional area of ​​the liquid reservoir decreases continuously is 5 mm or more and 30 mm or less, and the tapered opening angle θ is 20° or more and 90° or less. Within this range, it is possible to suppress the increase in tension when passing through the narrowed portion. In addition, it is preferable to process the boundary between the tapered part of the resin reservoir and the narrowed part to have a radius of 0.5 mm or more. If there is a corner at the boundary between the resin reservoir and the narrowed part, it will cause fuzzing. It is preferable that the length I of the narrowed part is 1 mm or more and 50 mm or less.As the length of the narrowed portion increases, the dimensional accuracy and single-fiber dispersion of the prepreg increases, but the frictional force at the narrowed portion increases, making fuzzing and breakage more likely to occur, resulting in reduced productivity. If the length of the narrowed portion is within the above range, it is possible to achieve both formability and productivity.

[0036] <Primary prepreg take-off tension> In the present invention, the tension T of the primary prepreg immediately after being pulled out of the die is preferably 0.3% or more and 7% or less of the tensile strength (N) per reinforcing fiber roving. Here, "immediately after being pulled out of the die" refers to the time during which the primary prepreg is present in the section after being pulled out of the die and before being introduced into the cooling nip roll or the additional impregnation device. If the tension T of the primary prepreg is less than 0.3% of the reinforcing fiber roving, sufficient impregnation effect cannot be obtained when the reinforcing fiber roving passes through the impregnation bar, and if it exceeds 7%, the occurrence of fluff due to rubbing during the process increases, resulting in a decrease in the quality of the prepreg and an increase in the frequency of breakage of the prepreg. More preferably, it is 1% or more and 5% or less. Here, the tension is measured using the PLS-KC series manufactured by Nidec-Shimpo Corporation. The rated load of the tension meter is appropriate to the tensile strength of the reinforcing fiber roving.

[0037] <Impregnation of the first prepreg> In the above-mentioned process for quantifying the weight of the thermoplastic prepreg, the more the amount of thermoplastic resin contained in the reinforcing fiber roving increases and swells, the more the amount of resin squeezed out at the narrowed portion increases. In the process of squeezing out the resin, the single threads in the reinforcing fiber roving are disturbed, and the resin pressure of the thermoplastic resin or the diagonal intrusion into the narrowed portion cause breakage of the single threads, which causes fluff. In addition, if the frequency of fluff generation increases, the fluff will clog the narrowed portion and lead to breakage of the prepreg body. On the other hand, the higher the void ratio in the reinforcing fiber roving, the more the voids in the reinforcing fiber roving will act as a buffer material to suppress breakage of the single threads, and the production speed can be increased. Therefore, in the present invention, the void ratio in the primary prepreg is controlled by adjusting the embrace angle and the impregnation distance in the impregnation process, and the resin is not impregnated into the reinforcing fiber roving more than necessary, thereby achieving both productivity and quality. In the present invention, the void ratio of the primary prepreg immediately after being pulled out from the die is preferably 0.1% or more and 15% or less. More preferably, it is 2% or more and 10% or less. If it is within the above range, it is possible to obtain a good molded product by applying heat and pressure when manufacturing a molded product using the thermoplastic prepreg. In addition, it is also possible to further increase the degree of impregnation of the prepreg itself by subjecting the primary prepreg pulled out from the die to additional impregnation.

[0038] The void ratio in the thermoplastic prepreg is obtained by observing a cross section perpendicular to the fiber direction in the prepreg as follows. The thermoplastic prepreg is embedded in epoxy resin "Epoquick" (registered trademark: manufactured by Buehler Co., Ltd.) and cured at room temperature for 24 hours, and then the sample is polished until the cross section perpendicular to the fiber direction of the prepreg can be well observed. The polished sample is photographed at a magnification of 300 times using an ultra-deep color 3D shape measuring microscope VHX-6000 (controller part) / VH-ZST (measurement part) (manufactured by Keyence Corporation). The photographed range is a range in which the entire cross section of the thermoplastic prepreg is captured. A joint image is photographed as necessary. In the photographed image, the total cross-sectional area of ​​the thermoplastic prepreg and the area of ​​the void portion are obtained, and the void ratio is calculated by (Equation 2). Void ratio [%] = 100 × (total area of ​​voids) / (total area of ​​thermoplastic prepreg) (Equation 2) <Removal device> In the present invention, it is preferable to place a take-off device for drawing out the thermoplastic prepreg from the die downstream of the process. This is because high friction and shear stress are generated between the reinforcing fiber roving and the thermoplastic resin in the die, and in order to overcome this and draw out the prepreg, it is preferable to generate a high take-off tension downstream of the process. As the take-off device, a nip roll, an S-shaped roll, a belt press, or the like can be used. In either case, slippage can be prevented and stable running can be enabled by increasing the frictional force between the device and the thermoplastic prepreg. For this purpose, it is preferable to arrange a material with a high friction coefficient on the device surface or to increase the pressing pressure on the prepreg. From the viewpoint of preventing slippage, a belt press is preferable.

[0039] <Prepreg impregnation process> In order to adjust the degree of impregnation to the desired level, it is also possible to combine a means for further increasing the degree of impregnation using an impregnation device after passing through the die of the present invention. Here, in order to distinguish from impregnation inside the die, additional impregnation after passing through the die is called impregnation, and the device for this purpose is called the impregnation device. It is desirable that the void ratio of the thermoplastic prepreg after impregnation is less than 2%. There is no particular limit to the device used as the impregnation device, and it can be appropriately selected from known devices depending on the purpose. For example, by using a device that applies pressure with heated nip rolls, the impregnation of the thermoplastic resin can be promoted by pressing between the rolls. The nip roll surface temperature, the linear pressure of the nip rolls, and the diameter and number of the nip rolls can be appropriately selected so as to achieve the desired degree of impregnation. In this case, it is preferable that the distance between the die and the impregnation device is short, because the impregnation can be performed before the temperature of the primary prepreg drops, and the heating device for reheating the primary prepreg can be omitted or simplified. In addition, by passing the prepreg through cooled nip rolls, it is possible to make small thickness adjustments and to improve the surface quality and dimensional accuracy of the final prepreg manufactured form.

[0040] <Thermoplastic prepreg width> There is no particular limit to the width of the thermoplastic prepreg, and it may be in the form of a tape with a width of several mm to several tens of mm, and the width can be selected according to the application. In recent years, in order to improve the efficiency of the lamination process of thermoplastic prepreg, devices called ATL (Automated Tape Laying) and AFP (Automated Fiber Placement) that automatically laminate narrow prepregs and prepreg tapes have become widely used, and it is also preferable to set the width to match this. In these devices, prepreg tapes of about 3 mm to about 25 mm are often used.

[0041] <Thermoplastic prepreg forming process> The prepreg after impregnation can be shaped into any shape depending on the purpose. In the above-mentioned production of thermoplastic prepregs, the thinner the thickness of the prepreg, the better the impregnation of the thermoplastic resin into the reinforcing fiber roving, which is desirable. Specifically, it is preferably 0.5 mm or less, and more preferably 0.2 mm or less. However, in the above-mentioned ATL and AFP devices, attempts have been made to make the prepreg thicker in order to increase the modeling speed. In addition, 3D printer devices (additive manufacturing) have also been attempted to model thermoplastic prepregs reinforced with continuous fibers, and are preferably used to model smaller parts than ATL / AFP. Therefore, in 3D printer devices, in order to reduce the curvature of the model, tape-shaped thermoplastic prepregs with narrow widths and thicknesses (widths of about 1 mm to 3 mm, thicknesses of about 0.3 mm to 1 mm) and thermoplastic prepregs with round cross sections with diameters of about 0.2 mm to 3 mm are preferably used. In the present invention, it is also possible to combine a process of forming the cross-sectional shape of the prepreg into an arbitrary shape after the additional impregnation process of the thermoplastic prepreg. Specific examples of shapes include a circle, an ellipse, a rectangle, and the like. As a shaping device, a known technique such as a drawing die in which holes are drilled into a metal block so that the cross-sectional area gradually decreases and the final cross section becomes the desired shape, or roll forming, in which a plurality of heated rollers having V grooves, U grooves, or concave grooves are arranged to gradually change the cross section, can be applied. EXAMPLES

[0042] <Mold> In the examples and comparative examples, the die, impregnation bar, liquid pool, and narrowed portion were configured as shown in FIG. 1. The material was stainless steel, and multiple cartridge heaters were inserted into each of the lower mold 24 and the upper mold 25, and PID control was performed with a K-type thermocouple so that the entire mold temperature was within the target temperature of ±5°C. A groove was provided on the side of the mold so that a maximum of 11 impregnation bars could be inserted, and the embrace angle was adjusted by changing the spacer thickness between the groove and the lower mold. Regarding the embrace angle, the embrace angles of the impregnation bar that first comes into contact with the reinforcing fiber roving when introduced into the die and the impregnation bar that last comes into contact with the reinforcing fiber roving in the die were set to the same embrace angle X, and in Table 1, this embrace angle X is the embrace angle per bar. The angle of the reinforcing fiber roving when introduced into the die was fixed at 30°, and the embrace angle of the first impregnation bar was 30° + X × 0.5. In addition, the impregnation bar that last comes into contact with the reinforcing fiber roving in the die returns the running angle of the reinforcing fiber roving to horizontal, so that its embrace angle is X × 0.5. The total embrace angle and total contact length of the impregnated bar is the sum of the embrace angle / contact length of all the impregnated bars.

[0043] The radius of the impregnated bar was r = 4mm, 10mm, and 20mm, and the width restriction was W = 4mm, 6mm, and 8mm. The angle θ of the liquid pool was 10° and 50°, and the length of the part where the cross-sectional area continuously decreases was H = 10mm, the length of the narrowed part was I = 2mm, the thickness J = 0.18mm, and the width L = 6mm were the same for all levels.

[0044] <Reinforced fiber roving> The thermoplastic prepreg was prepared by using two carbon fibers (Toray Industries, "TORAYCA (registered trademark)" T700S (12K)) as reinforcing fibers. The tensile strength of one T700S (12K) roving is 2180N.

[0045] <Matrix resin> The matrix resins used were nylon 6 (Toray, "Amilan (registered trademark)") and PPS (Toray, "Torelina (registered trademark)"). The viscosity of nylon 6 at 275°C is 32 Pa s, and the viscosity of PPS at 330°C is 142 Pa s.

[0046] <Tension setting> Before the evaluation of continuous runnability, the reinforcing fiber roving was pulled out from the bobbin hung on the creel at a speed of 0.5 m / min, and the tension just before entering the die was measured for a total of 3 minutes with a sampling interval of 0.5 seconds, and the brake mechanism of the creel was adjusted so that the average value was 500 cN ± 50 cN.

[0047] <Evaluation of continuous running performance> To evaluate the continuous runnability of the thermoplastic prepreg, it was run continuously for 60 minutes at a speed of 5 m / min. Thermoplastic prepreg without breakage or fluff on the surface was rated as "○", prepreg without breakage but with a small amount of fluff on the surface was rated as "△", and prepreg with breakage was rated as "×".

[0048] <Evaluation of void ratio> In the examples and comparative examples, in order to see the effect of the impregnation bar and the resin reservoir, the thermoplastic resin was solidified by air cooling without additional impregnation or passing through a cooling nip roll, and the primary prepreg was wound up. Two reinforcing fiber rovings were run in parallel, one for void evaluation, and the other for tension measurement of the primary prepreg immediately after it came out of the die. The tension measurement of the primary prepreg was also measured for a total of 3 minutes with a sampling interval of 0.5 seconds, and the average value was taken as the tension under those conditions. In addition, prepregs for void evaluation were taken from points 1 m, 2 m, and 3 m from the start and end points of the sample that had been evaluated for 60 minutes of runnability. The average value of the void ratios at the above six points was taken as the void ratio under those conditions.

[0049] The void ratio in the thermoplastic prepreg is obtained by observing the fiber direction and the vertical cross section in the prepreg as follows. The thermoplastic prepreg is embedded in epoxy resin "Epoquick" (registered trademark: manufactured by Buhler Co., Ltd.) and cured at room temperature for 24 hours, and then the sample is polished until the fiber direction and the vertical cross section of the prepreg can be well observed. The polished sample is photographed at a magnification of 300 times using an ultra-deep color 3D shape measuring microscope VHX-6000 (controller part) / VH-ZST (measurement part) (manufactured by Keyence Corporation). The photographed range is the range in which the entire cross section of the thermoplastic prepreg is captured. A joint image is photographed as necessary. In the photographed image, the total cross-sectional area of ​​the thermoplastic prepreg and the area of ​​the void portion were obtained, and the void ratio was calculated by (Equation 2). Void ratio [%] = 100 × (total area of ​​voids) / (total area of ​​thermoplastic prepreg) (Equation 2) In Table 1, a void rate of less than 5% is marked as "◎", 5% to 10% is marked as "〇", 10% to 15% is marked as "△", and 15% or more is marked as "×".

[0050] <Prepreg surface quality> Among the samples that were evaluated for 60-minute continuous running performance, those with excellent surface quality of the thermoplastic prepreg were rated as "○", those with a small amount of fluff on the surface or folded edges were rated as "△", and those with fluff on the surface or cracks in the prepreg were rated as "×". Those in which the prepreg was broken were rated as "-".

[0051] Example 1 Thermoplastic prepregs were produced under the following conditions: radius of impregnated bar r = 10 mm, included angle per impregnated bar 40°, number of impregnated bars 5, total included angle 190°, total contact length 33.2 mm, taper angle of liquid pool θ = 50°, width of width regulation W = 6 mm, resin used was nylon 6 (32 Pa s). The tension of the first prepreg was T = 4285 cN (1.97% per reinforcing fiber roving), and the void ratio was 6.1%. Continuous runnability was good, and the surface quality of the obtained prepreg was good.

[0052] Example 2 Thermoplastic prepregs were produced under the following conditions: radius of impregnated bar r = 20 mm, included angle per impregnated bar 20°, number of impregnated bars 9, total included angle 190°, total contact length 66.3 mm, taper angle of liquid pool θ = 50°, width of width regulation W = 6 mm, resin used was nylon 6 (32 Pa s). The tension of the first prepreg was T = 8392 cN (3.85% per reinforcing fiber roving), and the void ratio was 2.5%. Continuous runnability was good, and the surface quality of the obtained prepreg was good.

[0053] Example 3 Thermoplastic prepregs were produced under the following conditions: radius of impregnated bar r = 10 mm, included angle per impregnated bar 40°, number of impregnated bars 5, total included angle 190°, total contact length 33.2 mm, taper angle of liquid pool θ = 50°, width of width regulation W = 4 mm, resin used was nylon 6 (32 Pa s). The tension of the first prepreg was T = 3426 cN (1.57% per reinforcing fiber roving), and the void ratio was 11.1%. Continuous runnability was △ with a small amount of fluff observed, and the surface quality of the obtained prepreg was △ with a small amount of fluff observed on the surface.

[0054] Example 4 The thermoplastic prepreg was produced under the following conditions: radius of the impregnated bar r = 10 mm, included angle per impregnated bar 40°, number of impregnated bars 5, total included angle 190°, total contact length 33.2 mm, taper angle of the liquid pool θ = 50°, width of width regulation W = 8 mm, resin used was nylon 6 (32 Pa s). The tension of the first prepreg was T = 9314 cN (4.27% per reinforcing fiber roving), and the void ratio was 2.2%. Continuous runnability was ◯, and the end of the obtained prepreg was △ with a small amount of folding observed.

[0055] Example 5 Thermoplastic prepregs were produced under the following conditions: radius of impregnated bar r = 10 mm, included angle per impregnated bar 40°, number of impregnated bars 5, total included angle 190°, total contact length 33.2 mm, taper angle of liquid pool θ = 10°, width of width regulation W = 6 mm, resin used was nylon 6 (32 Pa s). The tension of the first prepreg was T = 5237 cN (2.36% per reinforcing fiber roving), and the void ratio was 5.6%. Continuous running was good, and the surface quality of the obtained prepreg was fair with a small amount of fuzz on the surface.

[0056] Example 6 Thermoplastic prepregs were produced under the following conditions: radius of impregnated bar r = 10 mm, included angle per impregnated bar 15°, number of impregnated bars 5, total included angle 90°, total contact length 15.7 mm, taper angle of liquid pool θ = 50°, width of width regulation W = 6 mm, resin used was nylon 6 (32 Pa s). The tension of the first prepreg was T = 2078 cN (0.95% per reinforcing fiber roving), and the void ratio was 13.8%. Continuous runnability was good, and the surface quality of the obtained prepreg was good.

[0057] Example 7 Thermoplastic prepregs were produced under the following conditions: radius of impregnated bar r = 10 mm, included angle per impregnated bar 60°, number of impregnated bars 5, total included angle 270°, total contact length 47.1 mm, taper angle of liquid pool θ = 50°, width of width regulation W = 6 mm, resin used was nylon 6 (32 Pa s). The tension of the first prepreg was T = 5964 cN (2.74% per reinforcing fiber roving), and the void ratio was 4.9%. Continuous runnability was △ with a small amount of fluff observed, and the surface quality of the obtained prepreg was △ with a small amount of fluff observed on the surface.

[0058] Example 8 Thermoplastic prepregs were produced under the following conditions: radius of impregnated bar r = 10 mm, included angle per impregnated bar 50°, number of impregnated bars 9, total included angle 430°, total contact length 75 mm, taper angle of liquid pool θ = 50°, width of width regulation W = 6 mm, resin used was nylon 6 (32 Pa s). The tension of the first prepreg was T = 9531 cN (4.37% per reinforcing fiber roving), and the void ratio was 2.2%. Continuous runnability was △ with a small amount of fluff observed on the surface, and the surface quality of the obtained prepreg was also △ due to a small amount of fluff observed.

[0059] Example 9 The thermoplastic prepreg was produced under the following conditions: radius of impregnated bar r = 10 mm, included angle per impregnated bar 40°, number of impregnated bars 5, total included angle 190°, total contact length 33.2 mm, taper angle of liquid pool θ = 50°, width of width regulation W = 6 mm, resin used PPS (142 Pa s). The tension of the first prepreg was T = 11394 cN (5.23% per reinforcing fiber roving), and the void ratio was 9.2%. Continuous running property was ◯, and the surface quality of the obtained prepreg was ◯.

[0060] Comparative Example 1 Thermoplastic prepregs were produced under the following conditions: radius of impregnated bar r = 4mm, included angle per impregnated bar 20°, number of impregnated bars 9, total included angle 190°, total contact length 13.3mm, taper angle of liquid pool θ = 50°, width of width regulation W = 6mm, resin used was nylon 6 (32 Pa s). The tension of the first prepreg was T = 1703cN (0.78% per reinforcing fiber roving), and the void ratio was 17.2%. Continuous running property was good, and the surface quality of the obtained prepreg was good.

[0061] Comparative Example 2 Thermoplastic prepregs were produced under the following conditions: radius of impregnated bar r = 10 mm, included angle per impregnated bar 60°, number of impregnated bars 11, total included angle 630°, total contact length 110 mm, taper angle of liquid pool θ = 50°, width of width regulation W = 6 mm, resin used was nylon 6 (32 Pa s). The prepreg broke about 5 minutes after starting. Tensile strength of primary prepreg T = 14152 cN (6.52% per reinforcing fiber roving), continuous runnability was ×. Because the prepreg broke midway, the void ratio and surface quality of the prepreg were not evaluated.

[0062] Comparative Example 3 The thermoplastic prepreg was produced under the following conditions: radius of impregnated bar r = 10 mm, included angle per impregnated bar 40°, number of impregnated bars 1, total included angle 30°, total contact length 5.2 mm, taper angle of liquid pool θ = 50°, width of width regulation W = 6 mm, resin used was nylon 6 (32 Pa s). The tension of the first prepreg was T = 672 cN (0.31% per reinforcing fiber roving), and the void ratio was 29.6%. Continuous runnability was good, and the surface quality of the obtained prepreg was good.

[0063] Comparative Example 4 Thermoplastic prepregs were produced under the following conditions: radius of impregnated bar r = 20 mm, included angle per impregnated bar 90°, number of impregnated bars 5, total included angle 390°, total contact length 136.1 mm, taper angle of liquid pool θ = 50°, width of width regulation W = 6 mm, resin used was nylon 6 (32 Pa·s). The prepreg broke about 1 minute after starting. Since sufficient sampling points could not be taken for the tension of the first prepreg, the average value up to 30 seconds after the start T = 16942 cN (7.7% per reinforcing fiber roving) was used as a reference value, and continuous runnability was ×. Since the prepreg broke midway, the void ratio and surface quality of the prepreg were not evaluated.

[0064] Example 10 Impregnation was performed by installing five heated nip rolls immediately after the prepreg was discharged from the die under the conditions of Example 1. The diameter of the nip rolls was 70 mm, the linear pressure was 100 N, and the temperature was 320° C. The surface quality of the obtained thermoplastic prepreg was good, and the void ratio was 0.7%.

[0065] [Table 1] [Industrial Applicability]

[0066] The thermoplastic prepreg according to the present invention can be molded into a desired shape by any method such as press molding, ATL, AFP, 3D printing, etc. Molded products obtained by molding the thermoplastic prepreg according to the present invention are useful for automotive applications such as aircraft engine peripheral parts, aircraft interior parts, aircraft exterior parts, vehicle frames, automobile engine peripheral parts, automobile underhood parts, automobile gear parts, automobile interior parts, automobile exterior parts, intake and exhaust system parts, engine cooling water system parts, and automobile electrical parts, as well as electrical and electronic part applications such as LED reflectors and SMT connectors. [Explanation of symbols]

[0067] 1a Reinforced fiber roving 1b 1st prepreg 1c Prepreg 2a Thermoplastic resin pellets 2b Thermoplastic resin in molten state 3. Hopper 4. Extruder 5 Gear pump 11 Creel 12 Change of direction roll 13 Cooling roll 14 Collection machine 15 Winder 21 Impregnated bar 21a Width regulation groove for impregnated bar 22 Liquid reservoir 23 Stenosis 24 Lower mold 25 Upper mold B Bottom surface of upper die C Bottom die apex L Width of the constriction W Width of impregnated bar Regulation width X: Reinforced fiber roving running direction Orthogonal to Y, X and Z Z vertical downward direction T Tension of the first prepreg r Radius of the impregnated bar H is the length of the part where the cross-sectional area of ​​the liquid pool decreases continuously I Length of the stenosis J Stenosis clearance θ Tapered opening angle of the liquid reservoir

Claims

1. A method for producing one prepreg from one reinforcing fiber roving by passing a reinforcing fiber roving horizontally or obliquely through a die to which a thermoplastic resin has been supplied, thereby imparting the thermoplastic resin to the reinforcing fiber roving, wherein the die is provided with a plurality of impregnation bars arranged in a direction perpendicular to the reinforcing fiber roving, and the reinforcing fiber roving is brought into contact with the impregnation bars to impregnate the reinforcing fiber roving with the thermoplastic resin, and the method for producing a prepreg satisfies the following conditions (a) to (c): (a) The radius r of the part where the impregnated bar comes into contact with the reinforcing fiber roving is 5 mm or more and 30 mm or less. (b) The included angle formed by the contact between the impregnated bar and the reinforcing fiber roving is 10° or more and 80° or less per impregnated bar. (c) The total included angle of multiple impregnated bars is 50° or more and 500° or less.

2. 2. The method for producing a prepreg according to claim 1, wherein the die is provided with a liquid reservoir portion whose cross-sectional area continuously decreases along the running direction of the reinforcing fiber roving impregnated with the thermoplastic resin and a narrowed portion having a slit-shaped cross section communicating with the liquid reservoir portion, and a tension T of the primary prepreg immediately after being pulled out of the die is 0.3% or more and 7% or less of a tensile strength (N) per one reinforcing fiber roving.

3. 3. The method for producing a prepreg according to claim 1, wherein the void ratio of the primary prepreg immediately after being pulled out from the narrowed portion of the die is 0.1% or more and 15% or less.

4. The method for producing a prepreg according to claim 1, wherein the viscosity of the thermoplastic resin at a melting point Tm+50°C is 1 to 500 Pa·s at a shear rate of 1216 sec-1.

5. 2. The method for producing a prepreg according to claim 1, wherein the total contact length between the reinforcing fiber roving and the multiple impregnated bars is 5 mm or more and 250 mm or less.

6. 3. The method for producing a prepreg according to claim 2, wherein a length H of a portion where the cross-sectional area of ​​the liquid pool continuously decreases is 5 mm or more and 30 mm or less, and a tapered opening angle θ is 20° or more and 90° or less.

7. 2. The method for producing a prepreg according to claim 1, wherein at least one of the plurality of impregnated bars has a groove for regulating the width of the reinforcing fiber roving.

8. The method for producing a prepreg according to claim 7, wherein the width L of the narrowed portion of the die and the restricted width W of the impregnation bar that finally contacts the reinforcing fiber roving inside the die satisfy the following formula (1). L×0.7≦W≦L×1.3 (1)

9. The method for producing a prepreg according to claim 1, further comprising the step of re-impregnating the primary prepreg drawn from the mouthpiece of the die.

10. The method for producing a prepreg according to claim 9, wherein the void ratio of the prepreg after the additional impregnation is less than 2%.

11. The method for producing a prepreg according to claim 9, further comprising a step of shaping the prepreg after the additional impregnation.

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