PREFORMED MATERIAL FOR FIBER REINFORCED PLASTICS

Abstract: A preformed material for use in fiber reinforced plastics is formed by laminating and integrally bonding a plurality of sheet-like substrates comprising reinforcing fibers (1, 3). At least one (4) of the laminated substrates is a woven fabric substrate having bonding material (2) composed of a thermoplastic polymer pre-adhering to the substrate (4) and extending substantially linearly along reinforcing yarns (1) or auxiliary filamentary yarns of the substrate. Due to the bonding material (2) the substrates of the preformed material are effectively bonded to each other even if the amount of the bonding material is small, no deterioration occurs in the arrangement and the distribution of the reinforcing fibers, no dislocation of the substrates occurs during a manufacturing process, and excellent characteristics of and a high productivity for forming the fiber reinforced plastics can be obtained.

Description: The present invention relates to a material preformed to a required shape for use in fiber reinforced plastics (hereinafter referred to as FRP) in order to reinforce a matrix resin of an FRP when the FRP is formed. Various methods for forming FRP are well known, and generally what type of method should be adopted is decided in accordance with required properties and output of production of an FRP. For instance, in the case where relatively high mechanical properties are required for an FRP but the number of products is small, an autoclave molding process is often adopted for the FRP. In the case where high mechanical properties are not required for an FRP but the number of products is relatively great, a hand lay up molding method is often adopted for the FRP. Further, a resin injection molding method for the case where the number of products is 500-1000 as a middle class of production scale, and a continuous pultrusion molding method where the number of products is more than the above number are generally adopted respectively. However, in the case where fibers, such as carbon fibers, which have a high strength and a high elastic modulus (Young's modulus) but are expensive are employed as reinforcing fibers for an FRP, the resin injection molding method and the continuous pultrusion molding method are not so often adopted. The reason why the methods are not so often adopted is that the arrangement or distribution of the reinforcing fibers tend to be disturbed when the FRP is formed, thereby decreasing the reinforcing effect according to high characteristic properties of carbon fibers etc., as described hereinafter. Therefore advantages according to use of carbon fibers etc. decrease. To explain the above problems in detail, a resin injection molding method is a method wherein, after dry sheet-like substrates composed of reinforcing fibers are laminated and charged into a cavity defined by male and female molds, a resin is injected into the cavity and the resin is impregnated into the substrates. The resin is then cured. In this method, the preformed material composed of laminated substrates tends to get out of shape, particularly when the substrates are laminated to a complicated shape. Moreover, there is a problem that the substrates are moved by the pressure applied when the resin is injected, thereby changing the laminated state of the substrates. This causes a disturbance of the arrangement or the distribution of the reinforcing fibers in the preformed material. A continuous pultrusion molding method is a method wherein sheet-like substrates are drawn from creels, a resin is impregnated into the drawn and laminated substrates, the substrates into which the resin is impregnated are shaped and the resin is cured by passing the substrates through a heated die, and the obtained FRP is then continuously drawn to a puller. Also in this method, a disturbance of the orientation or the distribution of the reinforcing fibers in the preformed material tends to occur on account of the deflection of the substrates due to the weight of the resin or the wrinkles of the substrates generated during the process, particularly after the resin is impregnated. On the other hand, the following preformed material is disclosed in page 402 of Plastic Processing Technology Handbook published on July 30, 1975 by Nikkan Kogyo Shinbunsha, a Japanese company. The preformed material is formed by laminating substrates composed of reinforcing fibers to a required shape and bonding the substrates to each other with chips made by cutting a substrate of reinforcing fibers in which a resin is impregnated or with powders of a thermoplastic material. However, this forming method also has a problem that the characteristic properties of carbon fibers etc. cannot be sufficiently obtained. Therefore, in the case where the chips are employed, non-uniform FRP tends to be obtained because the volume fraction of fibers contained in the portion of the FRP where the chips are becomes locally higher than in other portions. Moreover, in the case where the substrates are composed of long fibers or filamentary yarns, since the short fibers of the chips exist between the substrates, stress concentrates at the portions where the chips are and the fracture of the FRP tends to begin from the portions relatively early. On the other hand, in the case where the thermoplastic powders are employed, since it is difficult to distribute the powder uniformly on the substrates, fairly large non-uniformity occurs in accordance with the distribution of the powders. Accordingly, in order to provide the laminated substrates with a necessary bonding strength required for a preformed material, the amount of the powders should be relatively large. Since the powders do not constitute the matrix of the FRP, however, the increase in the amount of the powders deteriorates the properties of the FRP. Furthermore, JP-A-58-39442 discloses a preformed material formed by disposing webs, composed of short heat-melting fibers and formed as a mat, a strip or a grid between a mat of glass fibers and a woven fabric of glass fibers, and bonding the mat and the woven fabric by melting the webs. However, this preformed material has problems similar to the problems in the aforementioned materials. Therefore, in the case where the web is formed as a mat wherein the short fibers are arranged in random directions on the surface of the mat, since such a mat ordinarily has a large non-uniformity in accordance with the distribution of the short fibers, it becomes necessary to increase the amount of webs used for providing a required bonding strength for a preformed material. Since the webs do not constitute the matrix of the FRP even if the webs melt, the increase in the number of webs causes a deterioration in the properties of the FRP. Moreover, with respect to a woven fabric, convex portions of the bending weaving yarns of the woven fabric are the most suitable portions for effective bonding. However, when the webs formed as a mat melt, the molten materials adhere not only to the convex portions but also to concave portions and mesh portions, that is, the portions where the weaving yarns do not exist. This causes a very great increase in the amount of the webs required and an adequate impregnation of a resin becomes difficult when an FRP is formed. In the case where the webs formed as a strip or a grid are employed, the arrangement of the short fibers is usually performed so as to form straps. Since it is extremely difficult to adapt the pitch of the straps to the pitch of the convex portions which are the most suitable portions for bonding, not only an effective bonding becomes difficult but also the amount of the webs increases in order to obtain an adequate bonding strength for a preformed material. There occur similar problems even if the short fibers are arranged in fine yarn-like shapes. The preformed material disclosed in US-A-4410385 is made by including thermoplastic fibers within the weave of reinforcing fibers, the thermoplastic fibers thus appearing as warp or weft threads in the material. In contrast to this, in the preformed material of the present invention, as described more fully below, thermoplastic polymer threads are spirally wound round the warp or weft threads, rather than being themselves used as warp or weft threads. In the case of non-crimp woven fabric, the thermoplastic polymer may be wound round the auxiliary yarns used to hold together superposed sheets of reinforcing fibers. An object of the present invention is to provide a preformed material for FRP in which (a) substrates of reinforcing fibers can be bonded to each other by fairly small amounts of bonding materials efficiently and with a sufficient bonding strength, (b) disturbances of the arrangement and distribution of the reinforcing fibers when the preformed material is formed as a required shape or when an FRP is molded can be minimised and (c) the content of any resin other than a matrix resin can be kept to a minimum value, thereby obtaining an FRP having excellent characteristics. Another object of the present invention is to provide a preformed material in which substrates of reinforcing fibers can be easily bonded to each other and can be easily manufactured even if the preformed material has a complicated shape, thereby achieving excellent productivity. A preformed material for use in FRP according to the present invention and according to claim 1 is a laminate of sheet-like substrates having reinforcing fibers, these substrates including at least one substrate which is a woven fabric provided with threads of a thermoplastic polymer bonding material spirally wound round warp and/or weft threads of the weave so as to extend at least in one direction of the weave and to appear on at least one surface of the substrate, the laminate being so arranged that the thermoplastic bonding material is present at the layer interfaces and bonds the layers together. In the case of non-crimp woven fabric, the thermoplastic polymer bonding material may be wound round auxiliary filamentary yarns. Preferably the thermoplastic polymer bonding material is caused to preadhere to the said woven fabric substrate before said woven fabric substrate is incorporated in the laminate. The preformed material may be a material wherein adjacent sheet-like substrates to each other are both woven fabric substrates which have been provided with the bonding material, or may be a material wherein one only of adjacent sheet-like substrates integrally bonded by bonding material is the woven fabric substrate which has been provided with the bonding material, the other being a sheet-like substrate composed of reinforcing fibers, which may be selected from the group consisting of a woven fabric, a mat of short fibers or a mat of long fibers such as a chopped strand mat, a continuous strand mat or a surface mat, or a felt. The reinforcing fibers used in a preformed material according to the present invention are the fibers which are ordinarily used as the fibers for reinforcing the resin of FRP, for example, carbon fibers, glass fibers, polyaramide fibers, silicon carbide fibers, alumina fibers, alumina-silica fibers or metallic fibers. Among these fibers, carbon fibers are the most preferable. Of course, more than two types of fibers may be mixed, as is often performed in conventional manufacturing methods. The reinforcing fibers employed in the present invention have a tensile strength of more than 250 Kg/mm² (2450 N/mm²) and a tensile elastic modulus (tensile Young's modulus) of more than 7 × 10³ Kg/mm² (69 × 10³ N/mm²). The thermoplastic polymer constituting the bonding material is a polymer having a relatively low melting point such as nylon, copolymerized nylon, polyester, vinylidene chloride and vinyl chloride. Among these polymers, copolymerized nylon, which can melt at the temperature of impregnation of a matrix resin such as an epoxy resin and which has good adhesion with the matrix resin, is the most desirable. Such copolymerized nylon can be selected from the group consisting of copolymerized nylon 6 and nylon 12, copolymerized nylon 6 and nylon 66, copolymerized nylon 6, nylon 66 and nylon 610 and copolymerized nylon 6, nylon 12, nylon 66 and nylon 610. The bonding material according to the present invention is employed only for the purpose of integrally bonding the substrates, and not as a matrix for FRP. Therefore, the amount of the bonding materials is preferably as little as possible. From this point of view, the amount of the bonding material pre-adhering to the woven fabric substrate in a preformed material according to the present invention is very small, in the range of 0.2 - 10 wt. %, preferably 0.2 - 4 wt. %, more preferably 0.2 - 1.5 wt. % of the reinforcing fibers, although the amount varies according to the arrangement, pitch or size of the warps and wefts, or the type of the bonding material which adheres thereto. The woven fabric may be formed, for example, by weaving monofilament yarns, multifilament yarns or slit yarns composed of a thermoplastic polymer together with the warps and wefts composed of reinforcing fibers, and then softening or melting the thermoplastic polymer yarns by heating. In a preformed material according to the present invention, the preferable cross sectional area of the reinforcing yarn of the woven fabric substrate is in the range of 0.03 - 0.60 mm², more preferably 0.10 - 0.40 mm². The preferable weight of the woven fabric substrate is in the range of 60 - 700 g/m², more preferably 150 - 300 g/m². If the weight is less than 60 g/m², the productivity is not so good because many woven fabric substrates must be laminated in order to obtain a preformed material with a required thickness, thereby increasing the manufacturing time. If the weight is more than 700 g/m², the crimp of the weaving yarns becomes large. The large crimp causes a large stress concentration in the FRP, thereby deteriorating the properties of the FRP. Thus such a large woven fabric weight is undesirable. The weave structure of the woven fabric substrate is preferably a plain weave from the viewpoint of a high utilization factor of the reinforcing fibers, but it may be another weave structure such as a twill weave or a satin weave. Also it may be a so called non-crimp fibrous structure, such as that disclosed in JP-A-55-30974 or U. S. Patent 4,320,160, which comprises: a yarn group A composed of a plurality of straight reinforcing yarns gathered in one direction parallel to one another in the form of a sheet, a yarn group B composed of a plurality of straight reinforcing yarns gathered in another direction parallel to one another in the form of a sheet, and auxiliary filamentary yarns integrally holding the yarn groups A and B. The preformed material according to the present invention is formed by laminating a plurality of sheet-like substrates so as to form a required shape. After the lamination, the bonding material composed of a thermoplastic polymer between adjacent substrates is heated, thereby integrally bonding the substrates as a result of the adhesive strength of the bonding material. The accompanying drawings illustrate several embodiments of the invention and together with the description serve to explain the principles of the invention. FIG. 1 is a schematic plan view of a woven fabric substrate according to the present invention; FIGS. 2-10 are schematic plan views of woven fabric substrates, showing various adhesive states of bonding materials in accordance with a woven fabric substrate having a plain weave structure according to the present invention; FIGS. 11 and 12 are schematic plan views of woven fabric substrates, showing bonding materials in accordance with a woven fabric substrate having a biased plain weave structure according to the present invention; FIG. 13 is a schematic plan view of a woven fabric substrate having a unidirectional biased plain weave structure according to the present invention; FIGS. 14 and 15 are schematic plan views of woven fabric substrates, showing various adhesive states of bonding materials in accordance with a woven fabric substrate having a twill weave structure according to the present invention; FIGS. 16 and 17 are schematic plan views of woven fabric substrates, showing various adhesive states of bonding materials in accordance with a woven fabric substrate having a satin weave structure according to the present invention; FIG. 18 is a schematic plan view of a woven fabric substrate having a non-crimp fibrous structure according to the present invention; FIGS. 19 and 20 are schematic plan views of woven fabric substrates having a biased non-crimp fibrous structure according to the present invention; FIGS. 21-25 are schematic views illustrating the weaving of the woven fabric substrate shown in FIG. 13, FIG. 21 being a perspective view, and FIGS. 22-25 being side views; FIGS. 26-28 are schematic side views of laminated woven fabric substrates showing different laminations according to the present invention; FIGS. 29-36 are schematic exploded perspective views of preformed materials showing typical lamination structures of woven fabric substrates; and FIGS. 37-41 are schematic perspective views of preformed materials according to embodiments showing typical configurations according to the present invention. The illustrated preferred embodiments of the present invention will be described hereafter referring to the accompanying drawings wherein like reference numerals refer to similar parts; First, how the bonding material composed of a thermoplastic polymer pre-adheres to a woven fabric substrate is explained with respect to typical types of substrates. In FIG. 1, a woven fabric substrate 8 is formed as a plain weave and comprises warps 1 and wefts 3 composed of multifilaments of reinforcing fibers. As shown in the figure, bonding material 7 composed of a thermoplastic polymer extends along the warps 1 so as to spirally wind around the warps. The bonding material 7 extends substantially linearly along the warps 1 as a whole. In the woven fabric substrates shown in Fig. 1, since the bonding material pre-adheres to the intersecting portions of the warps 1 and the wefts 3, the warps and the wefts are bonded by the bonding material and the adhesion between the warps and the wefts can be sufficiently maintained. By this effect, the loosening of the substrate can be prevented when it is treated or cut. Although the bonding material is shown as pre-adhering to all the warps 1, it may pre-adhere to the warps or the wefts at intervals of a plurality of yarns, for example, on every second yarn or every third yarn. Further, the bonding material may extend along both the warps and the wefts. Thus, the bonding materials extend along at least one of the warps and wefts, substantially linearly and continuously or intermittently. If the woven fabric is heat-treated at a temperature higher than 80°C and lower than the melting point of the thermoplastic polymer yarns, then, since the heating is performed at a temperature lower than the melting point, the thermoplastic polymer yarns are softened but not melted, and the fixing of the warps 1 and the wefts 3 by the bonding material 7 does not proceed very far. If the substrate is heated at a temperature between the melting point of the thermoplastic polymer yarns and 20°C above the melting point, the thermoplastic polymer yarns begin to melt and the bonding material locally extends intermittently, although it extends substantially linearly as a whole. Since the heat treatment temperature is relatively low, even if it is higher than the melting point, the bonding material does not invade into the warps 1 or the wefts 3 and affect the appearance of the material on the surface of the substrate 8. If the substrate is heat-treated at a temperature between 20° and 50°C above the melting point of the thermoplastic polymer yarns, then, in this case also, the thermoplastic polymer yarns melt and the bonding material locally extends intermittently, though it still extends substantially linearly as a whole. However, since the heat treatment temperature is fairly high, part of the bonding material invades into the warps 1 and/or the wefts 3. The substrate in this state may be used in the present invention, but it is undesirable because, as part of the bonding material has invaded into the warps 1 and the wefts 3, the amount of the bonding material appearing on the surface of the substrate has decreased accordingly. If the substrate is heat-treated at a temperature higher than 50°C above the melting point of the thermoplastic polymer yarns, a large amount of bonding material invades into the warps and wefts and only a small amount appears on the surface of the substrate, so such a substrate is undesirable as a substrate for a preformed material because the bonding ability of the substrate becomes very low. Fig. 2 illustrates more schematically the substrate 8 shown in Fig. 1. Bonding material 7 adheres so as to spirally wind around the warps 1 and extends continuously. In the substrate 314 shown in Fig. 3, in comparison with the substrate 8 shown in Fig. 2, bonding material 214 extends intermittently. In the substrate 315 shown in Fig. 4, in comparison with the substrate 8 shown in Fig. 2, bonding material 215 adheres to every second warp 1. In the substrate 316 shown in Fig. 5, in comparison with the substrate 315 shown in Fig. 4, bonding material 216 extends intermittently. In the substrate 317 shown in Fig. 6, bonding material 217 adheres to the wefts 3 so as to spirally wind around and extend continuously along the wefts. In the substrate 318 shown in Fig. 7, in comparison with the substrate 317 shown in Fig. 6, bonding material 218 extends intermittently. In the substrate 319 shown in Fig. 8, in comparison with the substrate 317 shown in Fig. 6, bonding material 219 adheres to every second weft 3. In the substrate 320 shown in Fig. 9, in comparison with the substrate 319 shown in Fig. 8, bonding material 220 extends intermittently. In the substrate 325 shown in Fig. 10, two bonding materials 225a and 225b adhere per warp 1 so as to spirally wind around the warp. The winding directions of the bonding materials 225a and 225b are preferably different from each other. Thus, bonding materials can pre-adhere to a woven fabric substrate composed of a plain weave fabric in various ways. Next, Figs 11 and 12 show embodiments in accordance with a biased plain weave fabric. Fig. 11 illustrates a woven fabric substrate 336 having a biased plain weave structure wherein warps 401 and wefts 501 are composed of multifilaments of reinforcing fibers and the wefts are biased so as to make an angle of 45° relative to the warps. The angle of intersection between the warps and wefts can he appropriately chosen from within the range - 90° to + 90°. In this substrate 336, bonding material 236 extends continuously along the warps 401 so as to spirally wind around the warps. In the substrate 337 shown in Fig. 12, bonding material 237 extends continuously along the wefts 501 so as to spirally wind around the wefts. In the above embodiments, bonding material may extend intermittently and may be situated on every second warp or weft. Next, Fig. 13 shows an embodiment in accordance with a unidirectional biased plain weave fabric. Fig. 13 illustrates a unidirectional biased plain weave fabric 344 which comprises wefts 502 composed of reinforcing fibers and auxiliary filamentary yarns 601 as warps. The wefts 502 extend in one direction and are biased by 45° relative to the auxiliary filamentary yarns 601. In this substrate 344, bonding material 244 extends continuously along the auxiliary filamentary yarns 601 so as to spirally wind around the auxiliary filamentary yarns. In the above embodiments, bonding material may extend intermittently and may be situated on every second auxiliary filamentary yarn. Next, Figs 14 and 15 show embodiments in accordance with a twill weave fabric. Fig. 14 illustrates a twill weave fabric wherein warps 403 and wefts 503 intersect at right angles and at intervals of two yarns. In this substrate 356, bonding material 256 extends continuously along the warps 403 so as to spirally wind around the warps. In the substrate 357 shown in Fig. 15, bonding material 257 extends intermittently along the wefts 503 so as to spirally wind around the wefts and the bonding material is situated on every second weft. Next, Figs 16 and 17 show the embodiments in accordance with a satin weave fabric. Fig. 16 illustrates a satin weave fabric wherein warps 404 and wefts 504 intersect each other at right angles, a warp or a weft is threaded firstly on one side of the fabric over four wefts or warps and is then threaded over one weft or warp on the other side. In this substrate 366, bonding material 266 extends continuously along the warps 404 so as to spirally wind around the warps. In a substrate 367 shown in Fig. 17, bonding material 267 extends intermittently along the warps 404 so as to spirally wind around the warps and the bonding material is situated on every second warp. In the above embodiments, bonding material may extend continuously or intermittently and may be situated on every second weft or warp. Next, Fig. 18 shows an embodiment in accordance with a woven fabric substrate having a non-crimp fibrous structure. FIG. 18 illustrates a so called non-crimp woven fabric, which comprises (a) a yarn group (A) 701a composed of a plurality of straight reinforcing yarns gathered in one direction parallel to one another in the form of a sheet, (b) a yarn group (B) 701b composed of a plurality of straight reinforcing yarns gathered in one direction parallel to one another in the form of a sheet, the sheet face of the yarn group B contacting the sheet face of the yarn group A and the reinforcing yarns of yarn group B intersecting the reinforcing yarns of yarn group A, and (c) auxiliary filamentary yarns 602a and 602b which integrally hold the yarn groups A and B so as to form the woven fabric. In this substrate 375, bonding material 275 adheres to the auxiliary filamentary yarns 602b so as to spirally wind around the auxiliary filamentary yarns, and extends continuously along the auxiliary filamentary yarns. In the above embodiment, bonding materials may extend continuously or intermittently and may be situated on every second yarn or every second group in accordance with the auxiliary filamentary yarns 602a or 602b, or the groups of reinforcing yarns defined by the auxiliary filamentary yarns. Next, Figs 19 and 20 show embodiments in accordance with a biased non-crimp woven fabric. An angle α between two yarn groups composed of reinforcing yarns gathered in two directions different from each other can be appropriately chosen from within the range -90° to +90°. Figs. 19 and 20 show a biased non-crimp woven fabric wherein α equals +45°, as an example. In the substrate 384 shown in Fig 19, two yarn groups 703a and 703b composed of reinforcing yarns 407 and 507 gathered in two different directions in the form of a sheet, are integrally held by auxiliary filamentary yarns 604a and 604b, and bonding material 284 adheres to the auxiliary filamentary yarns 604b so as to spirally wind around the auxiliary filamentary yarns and extends continuously along the auxiliary filamentary yarns. In the substrate 386 shown in Fig 20, bonding material 286 adheres to the auxiliary filamentary yarns 604a so as to spirally wind around the auxiliary filamentary yarns and extends continuously along the auxiliary filamentary yarns. In the above embodiments, bonding material may extend continuously or intermittently and may be situated on every second yarn or every second group in accordance with the auxiliary filamentary yarns 602a or 602b, or the groups or reinforcing yarns defined by the auxiliary filamentary yarns. In such non-crimp woven fabrics as shown in Figs 18 to 20, the function of auxiliary filamentary yarns is to integrally hold groups of reinforcing yarns extending in one or two directions and to provide a substrate with a certain shape. The elongation at break of auxiliary filamentary yarns is preferably greater than that of reinforcing yarns. Since properties of FRP such as strength and elastic modulus become larger in proportion to the increase in the volume of reinforcing fibers, it is desirable to reduce the cross sectional area of an auxiliary filamentary yarn to as small as possible and to increase the amount or reinforcing fibers per unit volume of FRP to as large as possible. The ratio of auxiliary filamentary yarns to reinforcing yarns in accordance with cross sectional area of yarns in a woven fabric substrate is preferably from 0.01 to 0.20. When reinforcing yarns or reinforcing yarns and auxiliary filamentary yarns are bonded by heating a bonding material composed of a thermoplastic polymer, the auxiliary filamentary yarns tend to shrink, whereas the reinforcing yarns virtually do not shrink. The large shrinkage of the auxiliary filamentary yarns is undesirable because snaking of the reinforcing yarns occurs, thereby decreasing the strength and elastic modulus of the FRP. To prevent the snaking of reinforcing yarns, the rate of thermal shrinkage of auxiliary filamentary yarns must not be greater than 2% under dry conditions at 150°C. As fibers for the auxiliary filamentary yarns satisfying the above requirements, for example, for a substrate comprising reinforcing yarns of carbon fibers, there can be used glass fibers and polyaramide fibers having an elongation at break larger than that of carbon fibers, or can be used carbon fibers having an elongation at break larger than that of the carbon fibers constituting the reinforcing yarns. Next, in Figs 21 to 25, typical methods for manufacturing woven fabric substrates according to the present invention are explained, in accordance with the woven fabric substrates shown in Fig. 1. In Figs 21-24, a manufacturing method for a woven fabric before heat treatment is described in accordance with the woven fabric substrate shown in Fig. 1. In this case, mail 43 of heald 41 and mail 44 of heald 42 are alternately arranged, and warp 1 is passed through each of the mails 43 and 44. To this warp 1, thermoplastic polymer yarn 7a is bound spirally. Thus, as shown in Fig. 22, a bobbin 45 of a warp 1 and a bobbin 46 of a thermoplastic polymer yarn 7a are prepared, the thermoplastic polymer yarn is joined to the warp sent through guides 47 and 48, the thermoplastic polymer yarn is automatically wound spirally around the warp by utilizing the twist due to the release of the thermoplastic polymer yarn. The warp 1 on which the thermoplastic polymer yarn 7a is spirally wound is passed through mail 43, another warp is passed through mail 44, and this is repeated. Then each of the warps 1 is passed through a corresponding reed 21. The shedding motion of the warps 1 and the insertion of the wefts 3 are performed as shown in Figs. 23 and 24. In Fig. 23, heald 41 is lifted, heald 42 is brought down, and the weft 3 is inserted into the shed formed between the sheets formed by the warps and thermoplastic polymer yarns. The reed plates are then beaten up. The actions shown in Figs 23 and 24 are repeated. Thus the woven fabric substrate 8a is obtained. As shown in Fig. 25, the woven fabric 8a is heated by a heater 24 after being passed around a guide roller 23. The thermoplastic polymer yarns 7a are softened or melted by the heating, after which the woven fabric 8a is lightly pressed between a pair of rollers 25 and 26, and thus a woven fabric substrate 8 according to the present invention is obtained. The obtained substrate 8 is wound onto a winding roller 27. Next, bonding of woven fabric substrates to each other or bonding of a woven fabric substrate to another type of substrate is explained. As shown in Fig. 26, a woven fabric substrate 61 comprised of reinforcing yarns of reinforcing fibers and having bonding material 63 composed of a thermoplastic polymer can be integrally bonded with a different type of substrate 62 not having such bonding material. Thus, by utilizing only the bonding material 63 in the woven fabric substrate 61, the bonding between both substrates can be achieved. This bonding and integrating of the substrates is completed by lamination and heating of the substrates as hereinafter described. As shown in Fig 27, by utilizing bonding material 63 on both surfaces, other substrates 62 can be bonded on both of the surfaces of the substrate 61. Of course, as shown in Fig. 28, woven fabric substrates 61 having bonding material 63 according to the present invention can be integrally bonded to each other. Such bonding and integrating of substrates is, for instance, performed as follows. The woven fabric substrates having bonding material and cut to required sizes are laminated, or woven fabric substrates having bonding material and other type of substrates not having bonding material are alternately laminated. In these laminations, molds are used if necessary. After lamination, the laminated substrates are heated by an iron to a temperature higher than the melting point of the thermoplastic polymer constituting the bonding material, and are pressed at an appropriate pressure. By this heating and pressing, the laminated substrates are bonded and integrated via the bonding material, and thus a preformed material according to the present invention can be obtained. When the lamination is carried out, the directions of the reinforcing yarns constituting the substrates are set to required directions. In the case where the thermoplastic polymer constituting the bonding material tends to adhere to the iron, a mold releasing paper such as a silicon paper can be used to prevent such adhesion. Next, typical embodiments of laminations of woven fabric substrates according to the present invention are explained in Figs. 29-36, in accordance with a lamination of seven sheets of woven fabric substrates. However, the lamination structure is not restricted to the structures shown in Figs 29-36. The yarn weaving directions of a plurality of laminated woven fabric substrates may be all the same, and the yarn weaving direction of at least one of a plurality of laminated woven fabric substrates may be different from the yarn weaving directions of other substrates. In Fig. 29, seven laminated substrates are all the same woven fabric substrates 121. The reinforcing yarns 122 snd 123 in all of the substrates 121 are arranged in the same directions at +45° and -45°, respectively, relative to the longitudinal direction 124 of the preformed material. Adjacent substrates are bonded to each other with bonding material of a thermoplastic polymer extending linearly. The bonding of adjacent substrates is not always performed over the whole surfaces thereof. Partial bonding on the surfaces may be adopted, for example, if only the central portions of the laminated substrates are bonded to each other. The end portions of the substrates can be opened after laminating and bonding and this is convenient to form, for example, flange portions of a beam with an I-shaped cross-section. Such a beam will be described later in Fig. 37. In a structure shown in Fig. 30, a central woven fabric substrate 125 is a substrate comprising reinforcing yarns 126 and 127 extending in directions at 0° and 90°, respectively. On both surfaces of the substrate 125 are laminated unidirectional woven fabric substrates 130 having reinforcing yarns 128 extending in a direction at 90° and auxiliary filamentary yarns 129 (indicated with a broken line, hereinafter illustrated in the same manner) extending in a direction at 0°. On the outsides of both substrates 130 are laminated biased woven fabric substrates 133 having reinforcing yarns 131 and 132 extending in directions at 0° and -45°, respectively. Biased woven fabric substrates 136 having reinforcing yarns 134 and 135 extending in directions at 0° and -45°, respectively, are laminated as the outermost substrates. In the preformed material having such a lamination structure, since the orientation and arrangement of reinforcing yarns is symmetric relative to the central sheet of the lamination, no deformation after forming or curing occurs. Moreover, since the directions of orientation of reinforcing fibers are at 0°, +45°, -45° and 90°, artificial isotropic mechanical properties can be obtained. In a structure shown in Fig. 31, a central woven fabric substrate 137 is a substrate comprising reinforcing yarns 138 and 139 extending in directions at 0° and 90°, respectively. On both surfaces of the substrate 137 are laminated unidirectional biased woven fabric substrates 142 having reinforcing yarns 140 extending in a direction at -45° and auxiliary filamentary yarns 141 extending in a direction at +45°. On the outsides of both substrates 142 are laminated unidirectional biased woven fabric substrates 145 having reinforcing yarns 143 extending in a direction at +45° and auxiliary filamentary yarns 144 extending in a direction at -45°. Woven fabric substrates 148 having reinforcing yarns 146 and 147 extending in directions at 0° and 90°, respectively, are laminated as the outermost substrates. In such a preformed material, no deformation occurs and artificial isotropic mechanical properties can be obtained as well as in the preformed material shown in FIG. 112. In a structure shown in Fig. 32 there are laminated seven identical woven fabric substrates 149. The directions of reinforcing yarns 150 and 151 in each of the substrates 149 are set at 0° and 90°relative to the longitudinal direction 152 of the preformed material. In a structure shown in Fig. 33, a central woven fabric substrate 152 is a substrate comprising reinforcing yarns 153 and 154 extending in directions at 0° and 90°, respectively. On both surfaces of the substrate 152 are laminated biased woven fabric substrates 157 having reinforcing yarns 155 and 156 extending in directions of at 0° and -45°, respectively. On the outsides of the substrates 157 are laminated biased woven fabric substrates 160 having reinforcing yarns 158 and 159 extending in directions at 0° and +45°, respectively. Woven fabric substrates 163 having reinforcing yarns 161 and 162 extending in directions at 0° and 90°, respectively, are laminated as the outermost substrates. In a structure shown in Fig. 34, a central substrate 164 is a biased woven fabric substrate comprising reinforcing yarns 165 and 166 extending in directions at +45° and -45°, respectively. On both surfaces of the substrate 164 are laminated woven fabric substrates 169 having reinforcing yarns 167 and 168 extending in directions at 0° and 90°, respectively. On the outsides of the substrates 169 are laminated biased woven fabric substrates 172 having reinforcing yarns 170 and 171 extending in directions at +45° and -45°, respectively. Woven fabric substrates 175 having reinforcing yarns 173 and 174 extending in directions of 0° and 90°, respectively, are laminated as the outermost substrates. In a structure shown in Fig. 35, there are laminated seven identical woven fabric substrates 176. The direction of reinforcing yarns 177 in each of the substrates 176 is set to the longitudinal direction of the preformed material, and the direction of auxiliary filamentary yarns 178 is set to a direction at 90°. In a structure shown in Fig. 36 three central subtrates 179 are biased woven fabric substrates comprising reinforcing yarns 180 and 181 extending in directions at +45° and -45°, respectively. On both outer surfaces of the three substrates are laminated two sheets of unidirectional woven fabric substrate 184 having reinforcing yarns 182 extending in a direction at 0° and auxiliary filamentary yarns 183 extending in a direction at 90°. Then, the preformed material of the present invention is formed to a desired shape, corresponding to the shape of the FRP to be formed, as will be explained below. Fig. 37 illustrates a preformed material for use in the formation of a beam of FRP with an I-shaped cross-section. The preformed material 71 is constructed of a lamination of woven fabric substrates integrally bonded to each other by bonding materials extending linearly and pre-adhered to the substrates. The preformed material 71 has an I-shaped cross-section and includes a web 72 and flanges 73. More particularly, the laminated material comprises a plurality of plain weave substrates composed of reinforcing fibers, for example four plain weave substrates 74A, 74B, 74C and 74D. These four substrates 74A, 74B, 74C and 74D are laminated such that warps 75 and wefts 76 thereof extend substantially at angles of +45° and -45°, respectively, with respect to the longitudinal direction of the preformed material 71 in the web portion of the I-beam and are integrally bonded to each other by the bonding material 77 which extends in the longitudinal direction of the preformed material 71. The substrates 74A, 74B, 74C and 74D are bent in such a manner that the two flange portions of substrates 74A and 74B and the other two flange portions of substrates 74C and 74D extend in opposite directions, to produce an I-shape. Two further plain weave substrates 78 composed of reinforcing fibers, which are different from the substrates 74A to 74D, are put on each of the upper and lower surfaces of the I-shaped beam such that warps 79 and wefts 80 thereof extend substantially at angles of 0° and 90°, respectively, and are integrally bonded to the substrates 74A, 74B and substrates 74C, 74D by bonding material 77 extending in the longitudinal direction of the preformed material 71. Adjusting material composed of reinforcing fibers 81 is inserted into each of the spaces formed between the substrates 74B, 74C and substrate 78 at the bent portions of the substrates 74A to 74D, with the fibers directed to extend in the longitudinal direction of the preformed material 71. Fig. 38 illustrates one variation of the above-illustrated preformed material. In Fig. 38, a preformed material 85 further includes a plurality of unidirectional woven fabric substrates 86, each having all reinforcing fibers directed to extend in the longitudinal direction of the preformed material 85 and each having a width of half the entire width of each flange of the I-beam. The substrates 86 are interposed in twos between the upper flange portion of the substrate 74B and the substrates 78, between the upper-flange portion of the substrate 74C and the substrates 78, between the lower-flange portion of the substrate 74B and the substrates 78, and between the lower flange portion of the substrate 74C and the substrates 78. Next, another embodiment of the preformed material will be explained with reference to Fig. 39. The preformed material 91 in accordance with this embodiment comprises a plurality of beams 92 having an I-shaped cross-section as was illustrated in Fig. 37 and skin materials 93 which are bonded to the upper and lower surfaces of the beams 92. Each skin material 93 is composed entirely of plain weave substrates composed of reinforcing fibers. Each skin material 93 comprises a lamination of a substrate 93A including warps and wefts arranged at angles of 0° and 90°, respectively, with respect to the longitudinal direction of the beam 92, a substrate 93B including warps and wefts arranged at angles of +45° and -45°, respectively, a substrate 93C including warps and wefts arranged at angles of 0° and 90°, respectively, a substrate 93D including warps and wefts arranged at angles of +45° and -45°, respectively, and a substrate 93E including warps and wefts arranged at angles of 0° and 90°, respectively. The substrates 93A to 93E are integrally bonded to each other by bonding material which linearly adheres to the substrates. The preformed material 91 thus constructed can be used for the formation of FRP structural members, for example, for aircraft. Fig. 40 illustrates a stiffening structure 114 as yet another embodiment of the present invention. In this embodiment, the stiffening structure 114 includes a base plate 112 composed of a triple-laminated structure of plain weave substrates 111 composed of reinforcing fibers, and a stiffener 113 for stiffening the base plate 112, which is also composed of a triple-laminated structure of plain weave substrates 111 composed of reinforcing fibers and is bent so as to have a U-shaped portion and flange portions extending from the ends of the legs of the U in directions away from the U-shaped portion. Each substrate 111 is integrally bonded to an adjacent substrate by bonding material extending linearly. The base plate 112 and the stiffener 113 are also bonded to each other by bonding material in the same manner as in the substrates 111. Such a stiffening structure can also be used for the formation of FRP stiffeners for aircraft. Fig. 41 illustrates a preformed material in accordance with yet another embodiment of the present invention and, more particularly, illustrates a preformed material 101 for use in the formation of a FRP T-type joint. The preformed material 101 is entirely composed of plain weave substrates composed of reinforcing fibers. The preformed material 101 comprises a substrate 102 including warps and wefts extending at angles of 0° and 90°, respectively, with respect to respective axes X-X and Y-Y, a substrate 103 including warps and wefts extending at angles of +45° and -45°, respectively, a substrate 104 including warps and wefts extending at angles of 0° and 90°, respectively, a substrate 105 including warps and wefts extending at angles of +45° and -45°, respectively, and a substrate 106 including warps and wefts extending at angles of 0° and 90°, respectively, which are arranged in the order 102, 103, 104, 105 and 106 from the inside of the T-joint and are integrally bonded to each other by bonding material composed of a thermoplastic polymer. Next, a method for producing a FRP member using the preformed materials illustrated above is described. First, the preformed materials are formed to a desired shape and are inserted into a mold. Then, a thermosetting resin at an A-stage or B-stage is injected into the mold and is impregnated into the preformed material. After the impregnation the resin is hardened by heating, that is, the resin is changed to the state of so-called C-stage, to produce an FRP having the shape of the preformed material. As the matrix resin of the FRP, for example, an epoxy resin, a non-saturated polyester resin, a phenolic resin or a polyimide resin can be used. According to the preformed materials in accordance with the present invention, the following effects can be obtained: Firstly, since the substrates of the substrates of the preformed materials are effectively integrally bonded to each other by the bonding material of a thermoplastic polymer, no deterioration will occur in the orientation and the distribution of the fibers and no dislocation of the substrates will occur due to the injected polymer when such an FRP is formed in a resin injection molding method. Further, when such an FRP is formed in a pultrusion molding method, no deformation and wrinkling will occur due to the weight of a polymer after its impregnation. As a result, desired orientation and distribution of reinforcing fibers can easily be obtained to provide an FRP having excellent characteristics. Secondly, since the bonding material for bonding the substrates together adheres linearly, the amount of the bonding material is made as small as possible and, further, since the bonding material is substantially different from the matrix of an FRP, the characteristics of the FRP do not deteriorate due to such bonding material. Thirdly, since woven fabric substrates are used in the preformed material, such a preformed material can easily be formed by, for example, an iron instrument, to enable a high efficiency of production even if the preformed material is of a complicated shape. In this connection, since the bonding material pre-adheres to the substrate by a very small amount, the draping property of the woven fabric substrates will not deteriorate to a great extent, which further increases the production efficiency. Accordingly, the preformed material according to the present invention can be formed to provide an FRP with a complicated shape, such as a chassis or a frame of a vehicle as well as FRP members as shown in Figs 37-41. Finally, by using a woven fabric substrate wherein warps and wefts are fixed with a thermoplastic polymer as shown in Fig. 1, not only does loosening not occur during handling or when the substrate is cut to make a preformed material, but also it becomes possible to maintain the original arrangement and distribution of the fabrics and to prevent the warps and the wefts from invading between the laminated substrates to deteriorate the characteristics of the FRP.

Claims: A preformed material for use in fiber reinforced plastics, said material being a laminate of sheet-like substrates having reinforcing fibers, these substrates including at least one substrate which is a woven fabric provided with threads of a thermoplastic polymer bonding material spirally wound round warp and/or weft threads of the weave (or, in the case of non-crimp woven fabric, round auxiliary filamentary yarns) so as to extend in at least one direction of the weave and to appear on at least one surface of the substrate, the laminate being so arranged that the thermoplastic bonding material is present at the layer interfaces and bonds the layers together. A preformed material according to claim 1, wherein the thermoplastic polymer bonding material is caused to preadhere to the said woven fabric substrate before said woven fabric substrate is incorporated in the laminate. A preformed material according to claim 2, wherein the thermoplastic polymer bonding material is caused to preadhere to the said woven fabric substrate by softening or melting the said thermoplastic. A preformed material according to any preceding claim, wherein the thermoplastic polymer bonding material appears in intermittent lines. A preformed material according to any preceding claim, wherein the said reinforcing fibers are selected from carbon fibers, glass fibers, polyaramide fibers, silicon carbide fibers, alumina fibers, alumina-silica fibers and metallic fibers. A preformed material according to any preceding claim, wherein in the said woven fabric substrate the bonding material is in the range of 0.2 to 10 wt % of the reinforcing fibers. A method of making a preformed material for use in fiber reinforced plastics, which comprises the steps of (a) making a number of sheet-like woven fabric substrates having reinforcing fibers, at least some of the fibers chosen from warp threads, weft threads and (in the case, of non-crimp woven fabric) auxiliary filamentary yarns having threads of a thermoplastic polymer bonding material wound spirally round them; (b) stacking the said substrates, if desired along with other substrates not having the thermoplastic polymer threads, ensuring however that thermoplastic polymer threads lie at the interfaces between substrates; and (c) bonding the substrates. A method according to Claim 7, with the additional step, between the said steps (a) and (b) of causing the thermoplastic polymer bonding material to adhere to the said substrate. A method according to Claim 8, wherein the said additional step is performed by softening or melting the said thermoplastic.

Inventors: KITO, KAZUO, NISHIMURA, AKIRA
Applicants: TORAY INDUSTRIES, INC.
Application year: 1987
Main classification: B29C67
IPC codes: D04H3, B29C70, C08J5, B32B5, B29K105, B29B11, B29D99