JP2008174605A - Fiber-reinforced resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a fiber-reinforced resin which considers the limit of a fiber-reinforced resin molded by a conventional general SMC, uses a reinforcing fiber bundle of short fibers in a specific range and readily develops mechanical properties such as a high degree of isotropy, a high strength, etc. <P>SOLUTION: The fiber-reinforced resin comprises a reinforcing fiber base composed of a group of a reinforcing fiber bundle of short fibers and a matrix resin composed of a thermosetting resin. The fiber bundle of the reinforcing fiber base in an amount of ≥90% is composed of a fiber bundle separated so as to make the number of single fibers of ≤100 and the number of straight fiber bundles is ≥70% the number of the total fiber bundles. The orientation of the fiber bundles is two-dimensionally pseudo-isotropy and the volume content of the reinforcing fiber is ≥35%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fiber reinforced resin, and in particular, to a fiber reinforced resin using a short fiber reinforced fiber and capable of expressing high strength.

  There are two types of fiber reinforced resins in which a resin is reinforced with reinforced fibers, one using a woven or unidirectional sheet made of continuous fibers as a reinforced fiber base, and one using reinforced fibers of short fibers. A fiber reinforced resin using a continuous fiber reinforced fiber base material has extremely high anisotropy such as strength characteristics, and is mainly applied to applications based on or using the anisotropy. . On the other hand, the fiber reinforced resin using a reinforced fiber base material composed of short fiber reinforced fibers can reduce this anisotropy, but depending on the manufacturing method, a considerable degree of anisotropy remains and can be expressed. There are limits to mechanical properties such as strength.

  A fiber reinforced resin molded by SMC (Sheet Molding Compound) is known as a representative fiber reinforced resin using reinforced fibers of short fibers. Reinforcing fibers (for example, carbon fibers) are industrially usually manufactured as fiber bundles (strands) of reinforcing fibers, and the number of single yarns is usually 1,000 (1K) in consideration of productivity and manufacturing cost. ) To 48,000 (48K) fiber bundles. In the SMC, a fiber bundle of such reinforcing fibers is used.

  In FIG. 6, the concept of the reinforced fiber base material in SMC is shown. That is, in SMC, while cutting a reinforced fiber bundle made of continuous fiber reinforced fibers to a predetermined length on a thermosetting resin film (sheet) in a semi-cured state, A reinforcing fiber bundle 51 made of reinforcing fibers is dispersed in random directions, and a resin is impregnated with a hot press to form a sheet, whereby a resin-impregnated reinforcing fiber substrate 50 is obtained (usually semi-cured resin and reinforcing fiber base). Prepreg form with the material 50). The reinforcing fiber base 50 is generally manufactured continuously. In such a SMC sheeting process, there is no process for opening and splitting the reinforcing fiber bundle, so that the fiber bundle of reinforcing fibers, like the fiber bundle 51 in the circle in the figure, has a single yarn. It is in a state where it is converged to the predetermined amount (1K to 48K) without being divided into fibers (that is, in a state of strands), and isotropic as the orientation state of the reinforcing fibers. The nature is low. However, since it is in a strand state and has high rigidity as a fiber bundle, the straight fiber length (the cut length) can be increased. On the other hand, fiber bundles impregnated with resin at the time of pressure molding, which is a feature of SMC, are flowed by pressing pressure together with low-viscosity resin, and the fibers are bent or bent at the curved surface, corners, corners, etc. There are many places to do. In addition, when the press pressure is forcibly increased in order to increase the volume content of the reinforcing fiber in order to improve the strength of the molded body, the fiber bundle is bent or broken even in the flat part due to bending due to the overlap of the fiber bundles. It tends to occur. When these fiber bundles are bent or broken, cracks that lead to breakage tend to develop from the site, and the strength of the fiber reinforced resin cannot be improved. That is, there is a limit to the strength improvement in the fiber reinforced resin molded by the conventional general SMC.

  In addition, since the SMC is a reinforcing fiber base material in a state of a bundle of fibers in which a large number of reinforcing fibers are bundled, it is difficult to close the reinforcing fiber bundles to a certain level or more (forcibly densely packed by pressing pressure). If you try to do so, the above-mentioned problem becomes remarkable). For this reason, the fiber volume impregnation rate usually does not reach 40%, and there is a limit to improving the strength by increasing the fiber volume impregnation rate. In addition, since each fiber bundle is a relatively thick fiber bundle made of single yarn of 1K or more, the resin portion between the fiber bundles becomes relatively large, and the bending or fiber breakage of the fiber bundle that becomes the starting point of breakage as described above. When this occurs, cracks that lead to breakage at the resin portion are more likely to progress. Also from this aspect, there is a limit to the strength improvement in the fiber reinforced resin formed by the conventional general SMC.

  Therefore, in view of the limitations of the conventional fiber reinforced resin formed by the general SMC as described above, the subject of the present invention is a highly isotropic grade using a reinforced fiber bundle of short fibers in a specific range, and An object of the present invention is to provide a fiber reinforced resin capable of easily expressing mechanical properties such as high strength.

  In order to solve the above-mentioned problems, the fiber reinforced resin according to the present invention is a fiber reinforced resin composed of a reinforced fiber substrate composed of a bundle of fiber bundles of short reinforced fibers and a matrix resin composed of a thermosetting resin. 90% or more of the fiber bundles of the reinforcing fiber base are composed of fiber bundles that are split so that the number of single yarns is 100 or less, and the number of straight fiber bundles is 70% or more of the total number of fiber bundles, The orientation of the fiber bundle is two-dimensionally quasi-isotropic, and the volume content of the reinforcing fibers is 35% or more.

  In the fiber reinforced resin according to the present invention, 90% or more of the fiber bundle of the reinforcing fiber base is composed of a fiber bundle that is split so that the number of single yarns is 100 or less, and is 1K or more in a conventional general SMC. In comparison, the fiber bundle is divided into fiber bundles having at least one order of number of single yarns. That is, if it is 100 or less in this way, a clear and sufficient significant difference can be given compared with the conventional general SMC. 90% or more of the fiber bundle is not particularly limited as long as the number of single yarns is 100 or less, and may be dispersed to a complete single yarn level. However, in reality, it is difficult to disperse all the fibers to a complete single yarn level in a state of being cut from a strand shape of 1K or more, so the number of single yarns is about 10 or more. Good.

  In the fiber reinforced resin according to the present invention, the ratio of the straight fiber bundle number to the total fiber bundle number is 70% or more, preferably 80% or more, more preferably 90% or more. The number of straight fiber bundles can be quantitatively measured by the measurement method described later.

  In addition, since the fiber reinforced resin according to the present invention aims at a more isotropic material, the orientation of the fiber bundle needs to be two-dimensionally quasi-isotropic. Whether it is pseudo-isotropic or not can also be determined by a determination method described later. Since the orientation of the fiber bundle is two-dimensionally quasi-isotropic, it becomes a fiber reinforced resin having much more uniform mechanical properties than a fiber reinforced resin molded by conventional SMC.

  Furthermore, in the fiber reinforced resin according to the present invention, the volume content of the reinforcing fiber is 35% or more, preferably 40% or more, more preferably 45% or more, and particularly preferably 50% or more. 90% or more of the fiber bundles are separated so that the number of single yarns is 100 or less, the number of straight fiber bundles is 70% or more of the total number of fiber bundles, and the orientation of the fiber bundles is two-dimensional. By being pseudo-isotropic, it is possible to achieve such a high fiber volume content without applying a particularly high press pressure, thereby easily exhibiting high mechanical properties.

  In the fiber reinforced resin according to the present invention, in particular, in order to ensure a high ratio of the number of straight fiber bundles and to secure a high fiber volume content, the fiber bundle is 95% or more of the fiber length of the reinforcing fibers. It is preferable that the carbon fiber exists in the range of 3 mm or more and 12 mm or less. In addition, the fiber bundle may include glass fibers in which 95% or more of the fiber length of the reinforcing fibers is in the range of 3 mm to 40 mm. Hybrid forms of these carbon fibers and glass fibers are also possible.

In the production of the fiber reinforced resin according to the present invention, it is particularly preferable to include a papermaking process. For example, it is preferable that the reinforcing fiber substrate is made of a reinforcing fiber substrate in which a fiber bundle is made by a paper making process and a basis weight is 100 g / m ² or more. By including such a papermaking process, good pseudoisotropy is ensured and a high fiber volume content is easily achieved. Especially, it is preferable that the said reinforced fiber base material consists of the reinforced fiber base material paper-made using the filtration net | network previously formed in the product shape or the expansion | deployment shape by batch papermaking.

  The fiber bundle splitting method in the fiber reinforced resin according to the present invention is not particularly limited. For example, the said fiber bundle can be set as the structure which consists of a fiber bundle opened with the card spinning machine.

  In the fiber reinforced resin which concerns on this invention, the combination form of the reinforced fiber base material which consists of a fiber bundle of the said reinforced fiber of a short fiber, and various reinforced fiber base materials is also employable. For example, another reinforcing fiber substrate made of continuous fibers (for example, a reinforcing fiber fabric made of continuous fibers or a unidirectional sheet material) is arranged on at least one side of the reinforcing fiber substrate made of a bundle of short fiber reinforcing fibers. It can be set as the installed structure. Another reinforcing fiber substrate made of such continuous fibers can be arranged, for example, for forming a surface layer of a molded body.

  When the fiber reinforced resin according to the present invention is molded into a predetermined shape, an RTM (Resin Transfer Molding) molding method can be typically employed, but an RFI (Resin Film Infusion) molding method can also be employed. .

  According to the fiber reinforced resin according to the present invention, a fiber bundle composed of a reinforced fiber base material and a matrix resin in which a mostly straight fiber bundle that has been split to a specific form is oriented with pseudoisotropy, and the reinforced fiber Since the volume content of is as high as 35% or more, high mechanical properties that cannot be obtained with a conventional fiber reinforced resin by SMC can be expressed uniformly.

Hereinafter, the present invention will be described in more detail with preferred embodiments.
The basic technical idea that led to the completion of the present invention will be described. When a load such as a bending load is applied to the reinforced fiber resin (FRP) molded body, most of the destruction of the material causes a crack from the end of the reinforcing fiber, and the crack eventually becomes a matrix around the end of the fiber. It propagates through the resin part and propagates to other fiber end parts in the vicinity, and finally crosses the molded body to cause total destruction. Therefore, if the end of another fiber does not exist near the end of a certain fiber where the crack has occurred, or if the ratio of the existing fiber is low, there is no target that the crack is likely to propagate, or the generated crack Therefore, the propagation effect of the generated crack is reduced, and the crack becomes difficult to grow any more. That is, the fracture resistance level of the molded body is increased, and as a result, the load resistance of the molded body is improved.

  However, when the reinforcing fiber is composed of short fibers, there are inevitably many fiber ends. Therefore, the crack generated at the end of the fiber propagates relatively easily toward the other end of the fiber along the matrix resin, and eventually the crack crosses the main body of the molded body. It will lead to destruction. However, if the reinforcing fiber exists so as to cross between the end of the fiber where the crack has occurred and the other end of the fiber nearest to which the crack propagates (that is, the end of the other reinforcing fiber If they are not located), the propagation of cracks is likely to be restrained by the reinforcing fibers, and the resistance level against “breakage” from crack generation to breakage is improved. That is, the load resistance of the molded body is improved (mechanical characteristics are improved).

  This concept will be described with reference to FIG. FIG. 1 shows a fiber bundle (A) having a crack (c) at the end (a) and a fiber bundle (B) having an end (b) closest to the end (a). A state is shown in which a predetermined number of fiber bundles that are not ends exist between the ends (between a and b). That is, in the aggregate of reinforcing fiber bundles in the three-dimensional orientation state in the fiber reinforced resin molded body, the crack (c) generated at the end (a) of a certain fiber bundle (A) Even if it is going to propagate in the direction of the end part (b) of the fiber bundle (B) through the matrix resin surrounding A), the fiber bundle between them (for example, referred to herein as “sound fiber bundle”). It shows a state where propagation is blocked and further progress is prevented. However, if the number of the healthy fiber bundles is less than a predetermined amount, the progress of cracks is not necessarily prevented and the possibility of progressing to destruction remains. In order to allow such a healthy fiber bundle to exist in a predetermined number or more, it cannot be achieved with a fiber bundle of 1K or more in the conventional SMC, and can be achieved only by reducing the number of single yarns of the fiber bundle to a certain number or less. Become. Based on this idea, in the present invention, in order to give a clear significant difference from the conventional SMC, the fiber bundle is defined as a split fiber bundle having a single yarn count of 100 or less compared to the conventional SMC. Has been. However, when splitting from strands of 1K or more, it is not realistic to set all the fiber bundles to 100 or less single yarns in this way. It was defined as a requirement that 90% or more of the fiber bundles had 100 single yarns or less.

  Moreover, in order to allow a predetermined number or more of healthy fiber bundles to exist between the fiber bundle end portions as described above, it is advantageous that each fiber bundle is as straight as possible without bending. That is, if the fiber bundle is bent, the end interval is inevitably shortened, and it becomes difficult to secure the number of healthy fiber bundles. Therefore, it can be said that it is advantageous to have a large number of straight fibers. However, even when all the fiber bundles are straight in the state of the base material before molding, the fiber bundles are caused to flow along with the flow of the resin at the time of resin impregnation, and deformation such as bending or bending may occur. However, in order to exert a high load resistance as described above, it is necessary that at least 70% or more is straight, and preferably a fiber bundle of 80% or more, more preferably 90% or more is straight. Is desirable. This also makes it possible to have a clear difference from the fiber reinforced resin by SMC.

  Here, the “straight fiber bundle” is determined by the following determination method. In the present invention, the “straight fiber bundle” determined by this method is 70% or more of the total fiber bundle. It is necessary to be.

The straight fiber bundle is determined according to the following definition.
(1) The fiber reinforced resin is heated at a temperature of 400 to 600 ° C. to burn off only the resin. At this time, care should be taken not to move the fiber due to hot air.
(2) A fiber bundle in a unit volume (a cube whose one side is three times the fiber length is appropriate) is extracted with tweezers or the like so that the form does not change.
(3) Next, the fiber bundle is passed through a cylindrical body having a length twice as long as the fiber length and inclined at about 60 ° C., and it is determined whether the fiber bundle naturally passes without applying a pressing force. A fiber bundle that has passed without stagnation is regarded as a “straight fiber bundle”.
However, the inner diameter of the cylindrical body is 2 mm for carbon fiber and 4 mm for glass fiber.
The above is a measurement method for a normal fiber bundle in which the fiber bundle is split into 100 or less single yarns. However, when the number of single yarns is 100 or more, such as SMC, the fiber bundle is directly attached because of the large diameter. Since it can be measured with a ruler, an uneven height of 4 mm or less at the inflection part was regarded as a “straight fiber bundle”.

  And, as described above, by setting the ratio of the fiber bundle having a single yarn number of 100 or less to 90% or more, compared to the case of using a reinforcing fiber base made of a group of fiber bundles of 1K or more in the conventional SMC, It becomes possible to increase the degree of isotropicity far. That is, in the present invention, the orientation of the fiber bundle is two-dimensionally quasi-isotropic, whereby uniform mechanical properties that cannot be obtained with a molded body by SMC can be obtained.

Here, whether or not “the orientation of the fiber bundle is two-dimensionally pseudo-isotropic” can be quantitatively measured in the present invention by the following method.
(Measurement method of fiber bundle orientation)
A reinforcing fiber substrate before resin molding or a reinforcing fiber substrate obtained by burning the resin after molding is projected on a plane with a circle whose radius is the reinforcing fiber length of short fibers (for example, 12 mm) ( (Viewed as a plan view), 360 ° of the circle is divided into 5 ° portions, and fiber bundles oriented in the direction within the angular range are divided into 80% or more within the angular range of each 5 ° portion. If present, it is defined that “the orientation of the fiber bundle is two-dimensionally quasi-isotropic”.

  The ratio of fiber bundles with 100 or less single yarns is 90% or more, straight fiber bundles are 70% or more of all fiber bundles, and the orientation of the fiber bundles is two-dimensional pseudo-isotropic. As a result, a volume content of reinforcing fibers of 35% or more can be easily achieved. The fiber volume content is preferably 40% or more, more preferably 45% or more, and particularly preferably 50% or more. With such a high fiber volume content, high mechanical properties can be easily expressed.

  In the fiber reinforced resin according to the present invention, the reinforcing fiber is a carbon fiber having a single yarn diameter of, for example, 5 to 20 μm (preferably 5 to 10 μm) and a length of 2 mm to 30 mm (particularly 3 to 12 mm is preferable). It is desirable to be in a state of being randomly oriented in the three-dimensional direction, and in particular to be in a quasi-isotropic orientation state as described above in the plane direction.

  The length is particularly important, and we aim to disperse it in the papermaking process, but the fiber dispersibility in the papermaking process has been split from the length exceeding 1/2 inch. Single yarns gather together to form pills, fiber bundles with more than 100 fibers, and terrible ones with 1000 or more tend to come together and tend to drop rapidly. There is a tendency that folds and bends occur frequently even though they are intertwined or even dispersed to a single yarn. Then, even if the number as the number of healthy fibers between the fiber bundle ends is satisfied, the aggregate only satisfies the number, and the function of blocking the original crack propagation is low, so it does not lead to improvement in strength after all. There is a fear. Therefore, it is preferable that 95% or more of the carbon fiber length of the short fiber is in the range of 3 to 12 mm.

  Further, glass fibers may be mixed in addition to carbon fibers, and their mixing ratio and length may be set according to the required characteristics of the application, but basically the same applies to glass fibers, and the length is 40 mm. The dispersibility reduction due to the occurrence of the above-described entanglement, pills, creases, etc. increases dramatically from above. Considering the relationship between the fiber diameter and the length, that is, the aspect ratio, the length of the carbon fiber is 3 to 12 mm, the length of the glass fiber is 3 to 40 mm (considering the hybrid configuration with the carbon fiber, It is preferable to set the length to 3 to 12 mm.) In order to ensure the desired fiber dispersibility necessary for strength improvement (in terms of prevention of fiber deformation and difficulty in entanglement). In particular, the ratio of tightening from the entire length of the fiber is desirably 100%, but it should be at least 95%, and conversely, if it is lowered, crack propagation from that portion becomes prominent, and the strength improvement effect May decrease rapidly. In addition, such a reinforced fiber hybrid is particularly suitable for applications that are difficult in terms of price.

  Further, as the reinforcing fiber constituting the reinforcing fiber base, in addition to the state of only the cut fiber of the short fiber, the continuous fiber base (for example, woven fabric, A unidirectional sheet or the like may be arranged. That is, it is effective to selectively dispose the continuous fibers on both side surface layer portions in a portion where particularly high bending stress acts. In some cases, the amount of continuous fiber substrate may be greater than the short fiber substrate.

  The matrix resin is a thermosetting resin having a relatively low viscosity, which is an essential requirement for RTM molding, and a low viscosity state in which the viscosity during flow is 3 poise (300 cm poise) or less is desirable.

  The fiber bundle (strand form) of the reinforcing fiber of the present invention is usually appropriately set according to the use from the production (economical) to the number of single yarns from 1,000 (1K) to 48,000 (48K). The fiber bundle is already known in the field of pulp and synthetic fibers in order to divide the fiber bundle into fiber bundles of 1/10 to 1 / several tens or less of single yarns of 100 or less and further disperse them in a random direction. The following paper making methods can be considered.

As the method, when the reinforcing fiber is carbon fiber,
A. In the wet method, there is a paper making method. That is,
(1) A carbon fiber bundle (strand; 1K to 48K yarn) is cut into a predetermined fiber length and stored. (2) A predetermined amount of the cut carbon fiber is put into a dispersion tank in which a surfactant or a thickener is added to water.
(3) The dispersion in the tank is agitated, and the single yarns in the strands adhered by the sizing agent adhering to the reinforcing fiber surface layer are separated from each other and dispersed.
(4) After dehydrating and filtering with an inclined net (called a wire), the binder is applied and then dried with hot air and taken off.
In addition, in the case of carbon fiber, the mesh opening of the inclined net is appropriate around # 60 to # 300 mesh, and is properly used depending on the fiber length and the thickness of the strand put into the dispersion tank.

B. In the dry method, there is a method of hanging on a card machine used in the spinning process.
(1) A carbon fiber strand (1K to 48K yarn) is cut into a predetermined fiber length and stored.
(2) A predetermined amount of the cut carbon fiber is put into a card machine and separated.
(3) If the splitting rate is low, hang it on the card machine again and split it to near the single yarn level.

In addition, the basis weight when the paper is separated with a paper machine or a card machine is also important. If it is produced with a comparatively low basis weight of 100 g / m ² or less as in the prior art, the number of laminated layers is increased in order to obtain a practical basis weight, resulting in a thicker base material and poor base material production efficiency, and the fiber volume of FRP. When a thick base material is pressed and condensed in order to increase the rate, problems such as bending and bending of the fiber occur. Therefore, in the present invention when manufacturing a substrate by the above method, the basis weight of greater than 100 g / m ² at least, preferably preferably produced in basis weight of 200 to 600 g / m ^2. When a high basis weight exceeding 600 g / m ² is used, when forming a product with a large unevenness and a complicated shape, the fiber bends when the base material is shaped into the shape because the fiber has a three-dimensional structure. Fiber disturbance such as breakage and breakage occurs. In particular, the smaller the radius of the corner of the curved surface, the easier it is to break and it is difficult to follow.

  In the present invention, as a form of the reinforcing fiber base material, for example, a base material formed of continuous fibers can be combined with a base material formed of only short fibers. When a relatively high bending load is applied, even the aggregate of short fiber reinforced fiber bundles with the appropriate number of healthy fibers is composed of only short fibers, so the surface layer on which the highest stress acts Has a limit in load capacity. Therefore, only the surface layer on which high stress acts is constituted by continuous fibers such as woven fabric, whereby reinforcement according to the magnitude of the load acting on each part is made and the proof stress is improved. For example, as shown in FIG. 2, it is costly to arrange a base material 62 (two layers each) made of continuous reinforcing fibers on the surface layers on both sides and to form only the intermediate layer with the base material 61 made of short fiber reinforcing fibers having the above-described configuration. A performance becomes high and it becomes the more practical hybrid fiber base material 60. FIG. Furthermore, each layer is bound with a binder such as PVA, and has an appropriate form retention property. In some cases, it is shaped into a predetermined shape before FRP molding, and there is no disorder of fibers during molding. Pre-treatment (preform) is performed.

  For example, the reinforcing fiber base dispersed to near the single yarn level is described above as being obtained by papermaking. However, in general mass production, a continuous papermaking base (product) is manufactured by a continuous papermaking facility, and a predetermined size is obtained. However, when the final product is FRP-molded with reinforcing fibers, the reinforcing fiber substrate is trimmed into a product shape in advance and then FRP-molded. In that case, since unnecessary base materials after trimming are discarded, there is a problem that the yield of the reinforcing fiber material is poor. Therefore, when making paper, if the paper is made in the shape of the final product or the developed shape, almost no reinforcing fiber material is discarded, so that the material yield can be greatly improved. A paper making apparatus for this purpose is illustrated in FIG. It is difficult to perform paper making by the above method, and it is necessary to carry out by a batch paper making method in which paper making is performed once as shown in FIG. In the batch paper making apparatus 70 shown in FIG. 3, the mixing and dispersing tank 71 is provided with a filtration net 74 (# 60 to # 300 mesh) for filtering reinforcing fibers on the bottom side, and a surfactant or thickener in water. And the like, and a strand of reinforcing fibers cut to a predetermined length are delivered from the fiber storage tank 72 and the dispersion liquid storage tank 73 by a predetermined amount. After they are delivered, the mixing and dispersing tank 71 is stirred in the tank by a stirrer 75, and the strands of reinforcing fibers are separated into a single yarn level in the tank. Thereafter, the cock of the discharge port 77 at the bottom is released, and all the dispersion in the mixing and dispersing tank 71 is discharged out of the tank. At that time, the reinforcing fibers are left as the paper base 76 on the filter screen 74, and the paper making is completed. Then, the lid is opened, the filter net 74 whose shape is formed into the final product shape and the paper-reinforced reinforcing fiber base material 76 are taken out from the tank, and an oven or the like is applied after appropriately applying a binder such as PVA (polyvinyl alcohol). Then, the reinforcing fiber base formed into a product shape is taken out. The discharged dispersion is returned to the storage tank and reused as much as possible.

  FIG. 4 shows a molding method in which FRP molding is performed with a thermosetting resin as a matrix resin, using a reinforcing fiber base 80 in a state where the number of healthy fiber bundles is dispersed to near the single yarn level. Indicates. That is, after the reinforcing fiber base 80 is disposed on the lower mold 82 having a cavity in the double-sided mold, the upper mold 81 is closed, and air in the mold is sucked from the suction port 83 to depressurize the mold cavity, An RTM molding method in which a thermosetting resin is press-fitted from an injection port 84 and impregnated into the reinforcing fiber base 80 and the resin is heat-cured will be described. When the short fibers are high density like this reinforcing fiber, that is, when the Vf (fiber volume content) is 40% or more, the flow resistance of the resin is high and impregnation becomes very difficult. An easy resin fluid medium may be added. Then, in order to make it easy to inject the resin injection directly into the easy resin flow medium, as shown in the drawing, the easy resin flow medium 85 is slightly protruded to the resin injection side from the reinforcing fiber base 80 and the protruded portion (illustrated When the resin injection port 84 is directly disposed in the groove portion (runner), the resin flow is smoothly performed from the beginning of the resin injection, and the resin impregnation proceeds efficiently. 4 denotes a sealing O-ring disposed between the upper die 81 and the lower die 82.

The easy resin flow medium has a resin flow characteristic lower than the resin flow resistance in the surface direction of the laminated substrate made of reinforcing fibers (for example, a flow resistance of 1/2 to 1/20 with respect to the reinforcing fiber laminated substrate). Almost anything can be applied as long as it is a medium, but it is necessary to select the material so that the adhesiveness and wettability with the matrix resin of the FRP molded product does not fall below a predetermined characteristic. Resin is preferable from the viewpoint of satisfying such characteristics and economical efficiency, but inorganic fiber reinforced fibers may be used. As the resin, a thermoplastic resin capable of forming a woven fabric or a non-woven fabric that can be easily configured to have a low flow resistance is optimal. In particular, a mat form composed of short fibers or continuous fibers, or a mesh-like woven fabric or the like is preferable. As the basis weight of the free-resin flow medium from the viewpoint of the resin filling amount is preferably in the range of 10~1500g / m ^2.

Specific materials include the following.
(1) Flame resistant yarn nonwoven fabric: carbon felt 50CF manufactured by TRUSCO NAKAYAMA Co., Ltd. (form of fabric: felted nonwoven fabric, basis weight: 680 g / m ² ).
(2) Continuous strand mat: manufactured by Nippon Sheet Glass Co., Ltd. (form of fabric: glass continuous fiber nonwoven fabric, basis weight: 300 to 600 g / m ² ).
(3) Glass fiber nonwoven fabric: Surface mat MF30P100BS6 manufactured by Nittobo Co., Ltd. (form of fabric: glass continuous fiber nonwoven fabric, basis weight: 30 g / m ² ). When applied, 5-15 ply is laminated.
(4) Chopped strand mat: “Glass Ron” CM manufactured by Asahi Fiber Glass Co., Ltd. (form of fabric: non-woven glass fiber, basis weight: 300 to 600 g / m ² ).
(5) Mesh fabric: Nylon Meshon NB20 manufactured by NBC (form of fabric: nylon plain fabric, thickness: 520 μm)

  FIG. 5 shows another FRP molding method. That is, a semi-cured thermosetting resin sheet 93 is laminated with the reinforcing fiber base 90 in pairs, and a mold (upper mold) heated to a temperature at which the resin is completely cured after being laminated in a predetermined number or more. 91, lower mold 92), which is a so-called RFI (Resin Film Infusion) hot press molding method. Compared to the RTM molding method, it is difficult to degas the base material, so there are drawbacks that voids and pinholes are likely to occur, but it can be easily molded simply by hot pressing with a press machine, There is a merit that facilities are unnecessary and a relatively light facility is sufficient. However, the degassing is considerably improved if the whole is covered with a film in a state where the resin sheet and the base material are laminated by external setup and vacuum suction is performed. In addition, it is also effective to form a molded product in the softened state in a low temperature atmosphere of 20 to 40 ° C. lower or lower than the resin curing temperature at the same time as degassing. Is. Furthermore, you may press with a vacuum bag and an autoclave by the same RFI shaping | molding.

  Table 1 shows the conditions and results of Examples and Comparative Examples. The matrix resins applied in the examples and comparative examples are all epoxy resins, and the form varies depending on the molding method, but there is no difference in physical properties.

<Example 1>
(1) Reinforcing fiber: Toray Industries, Inc. carbon fiber “Torayca” T700SC × 12K, cut length = 8 mm
(2) Substrate dispersion method: As a wet dispersion method, fibers are opened to near the single yarn level in the papermaking process, and more than 90% are straight fibers, and entanglement, bending, bending, etc. of fibers are The ratio was 5% or less of the whole.
Fabric weight / layer: 150 g / m ² , binder; PVA.
The number of single yarns in each fiber bundle is not more than 20 / bundle, and the number of healthy fiber bundles between the ends of each fiber bundle is about 150% or more of the single yarn and is 95% or more of the total. It was confirmed.
(3) FRP molding: RTM molding method is applied. The shape and method were as shown in FIG. 4, and the molding temperature was 100 ° C.
Eight layers of the base material (2) were laminated, and the following easy resin flow medium was disposed in the middle.
The fiber volume content excluding the easy resin flow medium part was molded at a plate thickness of 50%.
Easy resin flow medium: NBC mesh fabric, nylon meshon NB20 (form of fabric: nylon plain fabric, thickness: 520 μm)
The FRP molded product was heated at about 500 ° C. to burn off the resin, and the result of analyzing the remaining reinforcing fibers was as shown in Example 1 in Table 1 and satisfied the present invention.

<Example 2>
(1) Reinforcing fiber: Carbon fiber (CF) “Torayca” T700SC × 6K manufactured by Toray Industries, Inc., cut length = 12 mm,
Nittobo glass fiber (GF) chopped strand CS13C-897, cut length = 13 mm (filament diameter = 10 μm)
(2) Substrate dispersion method: As a dry dispersion method, the fiber was opened to near the single yarn level with a card machine. The ratio of carbon fiber to glass fiber was 2: 1 by weight.
Basis weight / layer = 400 g / m ² , binder; PVA.
The number of single yarns in each fiber bundle was not more than 50 / bundle, and most were just straight fibers, and the fibers were intertwined, bent or bent, and the volume ratio was 3.5% or less.
Further, it was confirmed that the number of healthy fiber bundles between the end portions of each fiber bundle was about 300% or more in terms of the number of single yarns was 90% or more.
(3) FRP molding: RFI molding method was applied. The shape and method are as shown in FIG.
Three layers of the substrate (2) above are laminated. As shown in FIG. 5, the epoxy resin sheet was laminated | stacked for every base material, and it hot-pressed and shape | molded with the metal mold | die heated at the temperature of 120 degreeC.
The epoxy resin sheet was adjusted to a thickness at which the fiber volume content was about 52% when the base material was impregnated with the resin (varies somewhat in the resin flow situation).
Table 1 shows the analysis results after the molded product was similarly heated to burn off the resin.

<Comparative Example 1>
(1) Reinforcing fiber: Carbon fiber “Torayca” T700SC × 12K manufactured by Toray Industries, Inc., cut length = 23-25 mm
(2) Substrate dispersion method: The fiber was opened to near the single yarn level by the same papermaking process as in Example 1.
Basis weight / layer = 400 g / m ² , binder: PVA.
The number of single yarns in each fiber bundle varied from 10 / bundle to 2K / bundle, and about 40% was 100 / bundle or more. In addition, tangling of fibers, pills, and bending of the fibers frequently occurred in various places (30% or more by volume ratio).
It was confirmed that the number of healthy fiber bundles between each fiber bundle end was from several bundles to about 100 bundles. (3) FRP molding: The same RTM molding method as in Example 1 was applied, and the method, procedure, and conditions were the same as in Example 1.
Eight layers of the base material of (2) above were laminated, and an easy resin flow medium exactly the same as in Example 1 was disposed in the middle.
The fiber volume content excluding the easy resin flow medium part was molded at a plate thickness of 50%.

<Comparative example 2>
(1) Reinforcing fiber: Toray Industries, Inc. carbon fiber “Torayca” T700SC × 12K, cut length = 18-20mm
(2) Base material dispersion method: Unlike conventional methods, a general SMC (Sheet Molding Compound) molding method was applied. First, an intermediate base material for SMC molding was implemented by the SMC molding apparatus applied at the time of the explanation of FIG.
On a thermosetting resin film, reinforcing fiber bundles (strands) are randomly sprinkled in a predetermined length while being cut (chopped) and impregnated into a fiber bundle cut by hot pressing to form a sheet (intermediate) Substrate). And the conveyed sheet | seat was cut | disconnected to predetermined length, and it laminated | stacked through the predetermined release paper.
Since this SMC sheet does not have a process of further opening and splitting the strands, almost all the fiber bundles are not split to the single yarn level, but are almost not split into a predetermined amount (12K = single). 12,000 yarns) were still in the state of strands converged. However, since it was in a strand state, the cut length was lengthened because the fiber bundle had high rigidity, but most of the shape remained straight before molding.
(3) FRP molding: A predetermined amount of the SMC substrate was used, and press molding was performed using the mold shown in FIG. The mold temperature was 160 ° C. and the press pressure was 80 kg / cm ² . The fiber volume impregnation rate was calculated to correspond to about 34%.
The resin was burned off at about 500 ° C. for the FRP molded body, and the state of the reinforcing fibers was observed. Although many fiber bundles were flowing together with the resin in the press molding, the fiber bundles were not unfolded much, and most of them remained at 12K, and even when dispersed, they were up to about 3K. Also, in many corners and corners, the fiber bundle that has flowed along with the resin flow is bent, and since the fiber bundle is dispersed in units, there is no other fiber bundle between the fiber bundle ends. From these results, several fiber bundles (thus, 12K to 30K) were present as healthy fiber bundles. However, there were many sites without any healthy fiber bundles, and thus no improvement in strength was expected.

  Table 1 shows the various conditions and physical property measurement results of the molded articles formed by FRP molding under the conditions described in the above Examples and Comparative Examples.

  From the above comparison results, if the dispersion state of the reinforcing fiber according to the present invention is achieved, the bending strength and the Izod impact value described for reference are large as compared with the conventional dispersion state as in Examples 1 and 2. Can be said to be improved.

  As described above, in the fiber reinforced resin according to the present invention, the reinforcing fiber is made of short fibers, so that it is easier to form into a product shape at the time of preforming before molding than a continuous fiber such as a woven fabric, and so-called near-near product shape. Net shape is possible, and the molding preparation process and the post-molding process (burr removal process) can be simplified. Further, the strength of the molded body is improved, and the strength that has been a problem of the short fiber configuration is greatly improved while exhibiting the strength close to that of a continuous fiber such as a woven fabric, although the short fiber configuration has the above effects. That is, cost performance is greatly improved.

  The fiber reinforced resin according to the present invention can be applied to sports equipment, automobile members, and general industrial applications having a three-dimensional shape. In particular, the more complicated the shape, the more superior to the conventional product.

It is explanatory drawing which shows the concept of the reinforced fiber base material in this invention. It is a schematic sectional drawing which shows an example of the lamination | stacking form of the reinforced fiber base material in this invention. It is a schematic block diagram of the batch papermaking apparatus which shows an example in the case of employ | adopting a papermaking process in this invention. It is a schematic sectional drawing which shows an example of RTM shaping | molding in this invention. It is a schematic sectional drawing which shows an example of RFI shaping | molding in this invention. It is a general | schematic fragmentary top view which shows an example of the reinforced fiber base material in the conventional SMC.

Explanation of symbols

A, B: Fiber bundle a, b: Fiber end c: Crack (crack)
50: SMC base material 51: Fiber bundle (strand)
60: Hybrid fiber base material 61: Short fiber base material 62: Continuous fiber base material 70: Batch paper making apparatus 71: Mixing dispersion tank 72: Fiber storage tank 73: Dispersion liquid storage tank 74: Filter net 75: Stirrer 76: Covered Papermaking base 77: Discharge port 80: Reinforcing fiber base material 81: Upper die 82: Lower die 83: Suction port 84: Injection port 85: Easy resin flow medium 86: O-ring 90 for sealing: Reinforcing fiber base material 91: Upper mold 92: Lower mold 93: Thermosetting resin sheet

Claims (9)

  A fiber reinforced resin comprising a reinforced fiber base material comprising a group of fiber bundles of short fiber reinforced fibers and a matrix resin comprising a thermosetting resin, wherein 90% or more of the fiber bundles of the reinforced fiber base material have a single yarn number. It consists of fiber bundles that have been split to be 100 or less, the number of straight fiber bundles is 70% or more of the total number of fiber bundles, the orientation of the fiber bundles is two-dimensionally pseudo-isotropic, and A fiber reinforced resin, wherein the volume content of the reinforced fiber is 35% or more.   The fiber reinforced resin according to claim 1, wherein the fiber bundle includes carbon fibers in which 95% or more of the fiber length of the reinforcing fibers is in a range of 3 mm to 12 mm.   The fiber reinforced resin according to claim 1 or 2, wherein the fiber bundle includes glass fibers in which 95% or more of the fiber length of the reinforcing fibers is in the range of 3 mm to 40 mm. The fiber reinforced resin according to any one of claims 1 to 3, wherein the reinforcing fiber base is made of a reinforcing fiber base made by making the fiber bundle in a paper making process and having a basis weight of 100 g / m ² or more.   The fiber reinforced resin according to claim 4, wherein the reinforcing fiber base is made of a reinforcing fiber base made by using a filter net formed in advance into a product shape or a developed shape by batch paper making.   The fiber reinforced resin according to any one of claims 1 to 5, wherein the fiber bundle is a fiber bundle opened by a card spinning machine.   The fiber reinforcement in any one of Claims 1-6 by which another reinforcement fiber base material which consists of continuous fibers is arrange | positioned by the at least one surface side of the reinforcing fiber base material which consists of a fiber bundle of the said short fiber reinforcement fiber. resin.   The fiber reinforced resin according to any one of claims 1 to 7, wherein the fiber reinforced resin is formed by an RTM molding method.   The fiber reinforced resin according to any one of claims 1 to 7, wherein the fiber reinforced resin is formed by an RFI molding method.

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