A method for manufacturing a shock resistant tool of fiber reinforced resin

Abstract: A method for forming a shock resistant tool comprising reinforcing fiber used as a reinforcing material and cyclopentadiene resin used as matrix resin by reaction injection molding method. Cyclopentadiene resin is superior in shock resistant performance and has a low melt viscosity, thus allowing fiber to be contained in the shock resistant tool at a high percentage.

Description: The invention relates to a method for manufacturing a shock resistant tool of fiber reinforced resin material by reaction injection molding in a die. The expression shock resistant tool as used in this description is intended to include any shaped article or product which in use is likely to be subjected to mechanical shocks and has to be capable to withstand such shocks. Typical examples of shock resistant tools in this meaning are: 1. Sporting goods such as a tennis racket frame, squash racket, badminton racket for absorbing a shock applied by a ball. 2. Sporting goods for absorbing a shock such as helmet; fencing plastron, fencing face-guard: crotch protecting tool; football shoulder protecting tool; ice hockey mask; ice hockey knee pad and elbow pad; soccer, squash racket, leg guards; ear protecting portion of water polo cap; horse saddle and the like. 3. Helmets for protecting head from accidental shock in riding car or bicycle, in construction work, and infant's play. 4. Bicycle frame, bicycle handle, canoe and the like for absorbing a shock and preventing breakage against a shock. 5. Protecting wall, against machine tool, for preventing the transmission of a shock. Description of the related art Conventionally, goods required to have a shock resistant performance are made of ABS resin, polycarbonate resin, fiber reinforced resin (FRP) formed by reinforcing thermoplastic resin with short fiber or fiber reinforced resin (FRP) formed by reinforcing thermosetting resin generally with chopped strand mat of glass. The chopped strand mat of glass may be replaced by continuous fiber, long fiber or short fiber consisting of glass fiber, carbon fiber, aramid fiber, boron fiber or ultra-high-molecular-weight polyethylene fiber. Unsaturated polyester resin is mainly used as matrix resin. The following methods are known for manufacturing the above fiber reinforced resins formed by reinforcing thermosetting resin with chopped strand mat of glass: a half-hardened prepreg formed by impregnating fiber with resin is cut to an appropriate size and a configuration, and then, cut materials are laminated on each other in a die, then, heated under pressure so as to harden the resin; chopped strand and resin are sprayed up in a die and then hardened; reinforced fibers are laminated on a balloon-shaped die, then, the reinforcing fiber is impregnated with resin and then, hardened. Comparing the above materials and manufacturing methods, shock resistant tools made of only ABS resin or polycarbonate resin do not have a favorable rigidity because they do not contain a reinforcing material. Compared with long fiber or continuous fiber, fiber reinforced resin (FRP) formed by reinforcing thermoplastic resin with short fiber has also an unfavorable rigidity. In the case of the fiber reinforced resin (FRP) formed by reinforcing thermosetting resin with chopped strand mat of glass, shock resistant performance of molded goods can be increased by using reinforcing fiber and matrix resin favorable in shock resistant performance and increasing the content percentage of reinforcing fiber. But it is difficult to increase the fiber content and the known methods for manufacturing the above shock resistant goods involve problems. The fiber content percentage can be increased by cutting the prepreg sheets having thermosetting resin impregnated therein to a certain configuration, laminating cut materials on a die, and heating them under pressure. But the so molded goods are inferior in shock resistant performance because thermosetting resin is inferior in shock resistant performance. In addition, this method has an unfavorable production cycle and moreover, the manufacturing cost is high. Further, in the spray-up method or bag method, glass fiber and unsaturated polyester are used in combination. These systems have the disadvantage that the resin does not penetrate through fine gaps between fibers, and voids are left between filaments. The disadvantage is attributed to the high viscosity of resin. When resin is injected at a high pressure to accelerate the permeation of resin between fibers, fiber are moved and twisted by the flow of resin. Thus, resin cannot be injected at a high pressure. Therefore, fiber cannot be contained at a high percentage in a shock resistant tool. For example, in commercial helmets the fiber contents is approximately 30% at most. Examples of documents disclosing pior art methods of the aforementioned type are the following: JP-A-2-302280 (DATABASE WPIL, no. 91-032865) discloses a method of molding a ski board by placing a core board wound with reinforcing fiber material in a mold and injecting a monomer or prepolymer into the mold which produces crosslinked polyesteramide or polydicyclopentadiene. US-A-4,708,969 discloses an injection molding method using reinforcing glas, graphite and/or aramid fibers and a cyclopentadiene resin as matrix resin. EP-A-0 344 693 discloses a method for making a reinforced polymeric structure by reaction injection molding using glas fiber fabric and an injection mixture for obtaining a polymerized dicyclopentadiene resin as matrix resin. Although this document discloses a glas fiber content as high as 60 weight-percent of the final product, it does not disclose any particular steps in the injection process for assuring complete penetration of the matrix resin into the fibers. As explained above, an attempt to increase the injection pressure in order to make the liquid resin penetrate the fibers results in the risk of the fiber layer becoming displaced and deformed. SUMMARY OF THE INVENTION It is an object of the invention to provide a method for manufacturing a shock resistant tool of fiber reinforced resin material by reaction injection molding in a die which makes it possible to obtain a shock resistant tool having a high fiber content and therefor a favourable shock resistance. According to the invention this object is achieved by a method as defined in claim 1. By the step of additionally compressing the injected reaction mixture and the fiber reinforcing material in the die, it is possible to make the reaction mixture to completely penetrate and impregnate the reinforcing fiber material in the die, even if such fiber material is present in a very high percentage. Since this additional compression step occurs after the injection of the reaction mixture into the die, the reaction pressure needs not to be extremely high and therefore the risk of displacing or deforming the reinforcing fiber material per-arranged in the die is avoided. The reaction injection molding method according to the invention uses at least one of the following reinforcing fibers: ultra-high-molecular-weight polyethylene fiber, carbon fiber, glass fiber, aramid fiber, alumina fiber, silicon carbide fiber, steel fiber, amorphous metal fiber, organic fiber and/or a combination thereof; cyclopentadiene resin is used as matrix resin. As the reinforcing fiber continuous fiber, long fiber or short fiber is used. When a high rigidity and a high strength are required, continuous fibers or long fibers are used. As an example of the reinforcing fiber material, cloth fiber, filament winding, a mat in random arrangement such as continuous strand mat are preferably used. Preferably, the fiber is contained in the shock resistant tool at more than 40% in a region in which the fiber is required to be contained at the highest percentage. Reinforcing fiber is contained therein at a varied percentage depending on a region, i.e., a region to which shock is mainly applied contains the reinforcing fiber at a high percentage and a region to which shock is applied in a small extent contains the reinforcing fiber at a low percentage. Thus, the shock resistant tool is light and its production cost is reduced. For example, in a shoulder protector for use in football, fiber is contained at 40% in the shoulder and 20% in the chest, portion. Preferably, nonwoven fiber is used in to the reinforcing fiber. It is preferable that only nonwoven fiber is used in a region in which a high strength is not required or nonwoven fiber is used at a percentage higher than the reinforcing fiber. It is also preferable to use nonwoven cloth allowing a smooth flow of resin during a molding operation and reducing the weight of the shock resistant tool, thus reducing cost, and this distributed at a varied percentage in different regions. For example, the flange of a baseball helmet may consist of nonwoven cloth. The following materials are used as the nonwoven cloth to be distributed in the outer side of the fiber reinforced resin and the surface of the inner side and/or intermediate portion thereof: glass fiber paper, carbon fiber paper, polyester nonwoven cloth, nylon nonwoven cloth, vinyl nonwoven cloth, ultra-high molecular-weight polyethylene nonwoven cloth, PPS nonwoven cloth, acrylic fiber nonwoven cloth and the like. Favorably, fiber density of the nonwoven cloth ranges from 1 to 35 vol% and more favorably from 2 to 20 vol% so that resin flows smoothly during a molding operation. Preferably, one or more kinds of fibers containing ultra-high molecular-weight polyethylene fiber is used as the reinforcing fiber. Shock resistant tools molded in a die by the reaction injection molding method according to the invention include sporting goods such as helmet, face-guard, pad, leg guards for protecting head, face, plastron, shoulder, elbow, knee and the like; racket frame such as tennis racket frame for use in ball games; helmets for protecting head from shock in riding car or bicycle and for construction work; vehicle frame including bicycle frame and bicycle handle, canoe frame for preventing breakage against a shock; and a protecting wall, against machine tool, for preventing the transmission of a shock. When the shock resistant tool is a racket frame, the racket frame contains ultra-high-molecular-weight polyethylene fiber at least 10 wt% in the reinforcing fiber and a resin layer including the nonwoven cloth in the inner portion, outer portion and/or intermediate portion of the fiber reinforced resin consisting of the cyclopentadiene resin reinforced with the fiber reinforcing material. In the the method for molding shock resistant tools, preferably, reinforcing fiber and nonwoven cloth are provided in the outer side, inner side and/or the gap between reinforcing material layers. The material thus preformed is placed in a die. Then, cyclopentadiene containing polymerization catalyst and initiator of polymerization is injected into the die, and the mixture is heated at a predetermined temperature, for example, lower than 130°C so as to mold it into crosslinked resin by two-solution injection molding method (RIM). According to the invention, after the reaction solution is injected, the preformed material is compressed against the surface of the die with sheet-shaped rubber shaped into the configuration in conformity with that of the die and the preformed material, and extra resin is discharged from a resin discharge opening. Thus, fiber content percentage is increased. In order to preform the material, the following methods are used: molding by means of a die; spray-up of short fiber and chopped strand mat; and molding by heating and pressure application of a reinforcing material to which a binder has been attached. As polymerization monomer used as the cyclopentadiene resin, dicyclopentadiene, dihydrodicyclopentadiene, tricyclopentadiene, tetracyclopentadiene, cyclopentadiene-methylpentadiene copolymer are used. As the polymerization catalyst, halide of tungsten, molybdenum, tantalum; oxyhalide; oxide; organic ammonium salt are preferably used. As the polymerization starting agent, organic metal compound, mainly alkyl of metal of I through III groups of periodic table, compounds of alcohol, phenol or the like are preferably used. Since a polymerization reaction is started very promptly in a solution containing the catalyst and activator, hardening may occur before a sufficient amount of solution flows into the mold. Therefore, monoether and/or monoester of a glycol compound selected from alkylene glycol or polyalkylene glycol are preferably used as an activity adjusting agent. In injection molding in the die, the die is heated at 40 to 130°C and polymerization reaction takes place for one to five minutes. The material of a shock resistant tool can be provided on a flexible core (internal pressure holding member) which conforms to the surface configuration of the die. Tube-shaped or bag-shaped materials such as nylon, cellophane, rubber, polyester, polyether ketone or the like is preferably used. As described above, a shock resistant tool made according to the present invention such as a racket frame or a helmet is formed in combination of reinforcing fiber and cyclopentadiene resin superior in shock resistant performance. Since cyclopentadiene resin to be used as matrix resin has a low melt viscosity, fiber can be contained at higher than 50%. Therefore, the shock resistant performance of the tool according to the present invention can be improved as compared with conventional ones. For example, comparing a helmet according to the present invention and a conventional helmet commercially available with each other, energy required to destroy the helmet according to the present invention is approximately twice as great as that required to destroy the conventional helmet. This data is obtained as a result of tests which is described later. Compared with the shock resistant performance of conventional tools, in addition to shock resistant performance, vibration damping performance, chemical resistant property, and weather resistant property are improved. When ultra-high molecular-weight polyethylene fiber and cyclopentadiene resin are used in combination, vibration damping performance is superior, so that vibration damping ratio can be made at a high percentage, namely, higher than 0.8%. Therefore, a tennis racket frame comprising the above mixture does not apply a great force to elbow, so that it can be preferably used by a less powerful players. Vibration damping characteristic is preferably provided by a layer consisting of 95% of matrix resin and 5% of nonwoven cloth, namely, a layer containing a high amount of resin and a small amount of nonwoven cloth. According to this distribution of ultra-high-molecular-weight polyethylene fiber and cyclopentadiene resin, the external appearance of a tool is preferable. Further, in the manufacturing method according to the invention, the material of the tool can be placed in a die by controlling the fiber angle, fiber amount, and fiber thickness. In addition, since the fiber reinforcing material is preformed, the molding cycle is favourable and an efficient productivity can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which: Fig. 1 is a plan view showing a tennis racket frame according to a first embodiment of the present invention; Fig. 2 is a sectional view taken along a line II-II of Fig. 1; Fig. 3 is a sectional view showing a first modification of the first embodiment; Fig. 4 is a sectional view showing a second modification of the first embodiment; Fig. 5 is a schematic view showing strength testing method according to the first embodiment; Fig. 6 is a schematic view showing a testing method for examining vibration damping characteristic according to the first embodiment; Fig. 7 is a diagrammatic view showing vibration damping waveform obtained by a vibration damping characteristic test; Fig. 8 is a perspective view showing a baseball helmet according to the second embodiment; Fig. 9 is a perspective view showing the baseball helmet viewed from bottom portion in Fig. 8; Fig. 10 is a plan view showing the cloth of reinforcing fiber to be used in the second embodiment; Fig. 11 is a perspective view showing a preforming method according to the second embodiment; Fig. 12 is a sectional view showing a molding die according to the second embodiment; Fig. 13 is a sectional view showing a modified manufacturing method; Fig. 14 is a front view showing a testing device for measuring the shock absorbing performance according to the second embodiment; and Figs. 15 through 22 are perspective views showing various examples of shock resistant tools according to the present invention. DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, an embodiment of the present invention is described below. Fig. 1 shows a shock resistant tennis racket frame 1. Its length ranges from 52cm to 68cm (68cm according to the first embodiment) and its weight ranges from 230g to 400g (335g according to the first embodiment). The vibration damping ratio of the tennis racket frame 1 is 0.8% which is greatly improved compared with conventional tennis rackets. As shown in Fig. 2, the tennis racket frame 1 comprises a core nylon tube 2 and a fiber reinforced resin layer 3 consisting of cyclopentadiene resin containing continuous fiber, consisting of ultra-high molecular-weight polyethylene fiber and carbon fiber, formed in the periphery of the core nylon tube 2. The racket frame 1 is manufactured by two-solution reaction -injection molding (RIM) method which will be described below. The core tube 2 is made of a nylon tube in the thickness of 100µm and braided carbon fiber (article number: BC-7664-24 (20), manufactured by Toho Rayon Co., Ltd.) is arranged in the periphery of the core nylon tube 2 so that each braided carbon fiber makes an angle of 24° with the longitudinal direction of the tennis racket frame 1 and the weight of the braided carbon fiber is 40 wt%. Braided fiber consisting of ultra-high-molecular-weight polyethylene fiber (SK-60, manufactured by Toyobo Co., Ltd.) is provided so that the braided fiber makes an angle of 24° with the longitudinal direction of the tennis racket frame 1 and the weight of the braided carbon fiber is 20 wt%. The carbon fiber and ultra-high-molecular-weight polyethylene fiber are braided and cut so that the angle of the braided fiber makes the above-described angle, and they are preformed so that the configuration of the braided fiber conforms to that of the tennis racket frame 1. The preforming method is described later in the description of a baseball helmet according to a second embodiment. The preformed fiber reinforcing material is arranged on the periphery of the core nylon tube 2. After the fiber reinforcing material is set in a die and the die is heated at 60°C the pressure in the die is reduced by a vacuum pump. Then, dicyclopentadiene containing polymerizing catalyst and initiator of polymerization is introduced in the die under pressure. The components for the desired amount of dicyclopentadiene are contained in two containers. Polymerizing catalyst is put into one container and an activator (initiator of polymerization) and an activity adjusting agent are put into the other container so as to prepare two stable reaction solutions. The reaction solutions are mixed with each other instantaneously by a mixing head of a two-solution reaction/injection molding device. The mixture is immediately injected into the die heated at 60°C under a low pressure. In the die, internal pressure is applied to the core nylon tube 2 during a time period of one to five minutes required to polymerize the mixture promptly. Thus, a hollow tennis racket frame as shown in Fig. 2 is obtained. Fig. 3 shows a first modification of the tennis racket frame of the first embodiment. The tennis racket frame 1' comprises the core nylon tube 2, a fiber reinforced resin layer 3 consisting of cyclopentadiene resin containing continuous fiber consisting of ultra-high-molecular-weight polyethylene fiber formed in the periphery of the core nylon tube 2, and a nonwoven cloth containing layer 4 consisting of cyclopentadiene resin containing glass nonwoven cloth formed in the periphery of the fiber reinforced resin layer 3. The length and weight of the tennis racket frame 1' are similar to those of the first embodiment, and the vibration damping ratio thereof is 2.5% which is improved greatly compared with conventional ones. The method for manufacturing the tennis racket frame 1' having the nonwoven cloth containing layer 4 is different from that of the first embodiment in that the glass nonwoven cloth is provided on the surface of the ultra-high-molecular-weight polyethylene fiber provided in the periphery of the core nylon tube 2 so that the weight percentage of the glass nonwoven cloth is approximately 5%. Fig. 4 shows a tennis racket frame 1" of a second modification of the tennis racket frame of the first embodiment. The tennis racket frame 1" comprises the nylon tuber core 2, an inner nonwoven cloth containing layer 5 consisting of cyclopentadiene resin containing glass nonwoven cloth formed in the periphery of the nylon tuber core 2, a fiber reinforced resin layer 3 consisting of cyclopentadiene resin containing continuous fiber consisting of ultra-high-molecular-weight polyethylene fiber formed in the periphery of the layer 5, and an outer nonwoven cloth containing layer 4 consisting of cyclopentadiene resin containing glass nonwoven cloth formed in the periphery of the layer 3. The configuration and weight of the tennis racket frame 1" according to the second modification are similar to those of the tennis racket frame 1 according to the first embodiment and the vibration damping ratio thereof is 3.5%. The method for manufacturing the tennis racket frame 1" according to the second modification is almost same as that of the first embodiment. Glass nonwoven cloth is arranged on the periphery of the nylon tube core 2, the continuous fiber layer consisting of ultra-high-molecular-weight polyethylene fiber is formed on the periphery thereof, and glass nonwoven cloth is arranged on the periphery thereof. The nonwoven cloth containing layer may be arranged as a middle layer, but it is preferable to arrange it on the surface of the tennis racket frame in view of the external appearance thereof. As the reinforcing fiber, ultra-high-molecular-weight polyethylene fiber and carbon fiber are used in the first embodiment, and only ultra-high-molecular-weight polyethylene fiber is used in the first and second modifications. But the following fibers may also be used in combination of ultra-high molecular-weight polyethylene fiber: glass fiber, aramid fiber, alumina fiber, silicon carbide fiber, steel fiber, amorphous metal fiber, organic fiber and/or a combination thereof. Preferably, the weight percentage of ultra-high-molecular-weight polyethylene fiber is more than 10 wt% of the reinforcing fiber material in view of vibration damping performance and shock absorbing performance. It is preferable that in addition to the nonwoven resin layer, the fiber reinforcing resin layer comprising cyclopentadiene resin contains reinforcing fiber made of a material formed in combination of the above-described materials or reinforcing fiber consisting of ultra-high-molecular-weight polyethylene fiber in 20 to 80 wt%. Experiment 1 The shock resistance performance, namely, the strength of the tennis racket frame of the above construction according to the present invention was compared with that of conventional tennis racket frames. The result is described below. As shown in Fig. 5, the tennis racket frame 1 was held upright by supporting both sides thereof with a supporting jig 15. A vertical load was applied to the tennis racket frame 1 at the top end thereof by a pressure applying device 16 provided above the tennis racket frame 1 so as to measure its destruction strength. The tennis racket frames of the first modification was used to compare shock resistant performance according to the present invention with conventional example tennis racket frames made of epoxy prepreg material and in the same configuration as the racket frame of the first modification. Embodiment 2 (four frames on average) 162kg Conventional B (four frames on average) 160kg It was confirmed that the strength of the tennis racket frame of the embodiment was higher than that of the conventional one. The vibration damping characteristic of the tennis racket frames of the present invention were compared with that of conventional tennis racket frames. Tests were conducted on the following embodiment (A) and conventional example (B). A: tennis racket frames according to the first embodi ment, the first modification, and the second modification (weight: 335g; length: 68cm) B: conventional tennis racket frames made of an epoxy prepreg material and having the same configurations as those of (A) Experiments for examining vibration damping characteristics were made by a device as shown in Fig. 6. The tennis racket frame 1 was hung by a string with its head portion 1a upward. An acceleration pick-up 12 was attached to one side of the tennis racket frame 1 at approximately the center between the head portion la and a gripping portion 1b. The other side of the tennis racket frame 1 was struck with an impact hammer 10. An FET analyzer 17 was connected with the hammer 10 and the acceleration pick-up 12. Vibrations generated when the tennis racket frame 1 was struck with the hammer 10 were received by the acceleration pick-up 12 and a signal was inputted to the FET analyzer 17. As a result, a graph as shown in Fig. 7 was obtained. In the graph, acceleration (α)/ force (F) is the ordinate and frequency is the abscissa. Vibration damping characteristics were calculated as Δω/2ωn. Vibration damping ratios were calculated based on the graph. The result was: First embodiment: ζ = 0.8% First modification: ζ = 1.2% Second modification: ζ = 1.6% The vibration damping ratio ζ of the conventional example (B) was 0.2% to 0.3% (10 tennis racket frames were used on average.) A test for examining the players' feeling for tennis ball hittings was conducted. Fifty players hit tennis balls with rackets of (A) and (B). The result is shown below. Persons who felt that (A) was better than (B) in vibration absorbing performance 46 persons Persons who did not judge which is better 4 persons A shock resistant baseball helmet according to a second embodiment of the present invention is described below. A baseball helmet 20 as shown in Figs. 8 and 9 comprises a head 20a and a flange 20b. The fiber reinforcing material of the head 20a consists of an ultra-high-molecular-weight polyethylene fiber cloth layer and a felt-like nonwoven cloth layer consisting of carbon fiber and ultra-high molecular-weight polyethylene mixed with each other. The ultra-high-molecular-weight polyethylene fiber cloth layer and the felt-like nonwoven cloth layer alternate with each other. The head 20a contains fiber in the percentage of 50 by volume. The flange 20b is made of a nonwoven cloth layer consisting of the carbon fiber and ultra-high-molecular-weight polyethylene and contains fiber in the percentage of 20 by volume. The fiber reinforcing material of the head 20a and the flange 20b is preformed. In case of the head 20a, the periphery of a ultra-high-molecular-weight polyethylene fiber cloth 21 as shown in Fig. 10 is cut in conformity with the surface 22a of a male die 22 of a helmet die as shown in Fig. 11 and surface-treated. A nonwoven cloth layer is laminated alternately on the surface of the ultra-high-molecular-weight polyethylene fiber cloth 21 similarly. These fiber layers are connected with each other by a binder. Thus, the fiber reinforcing materials of the head 20a are integrated with each other by alternating a desired number of both layers with each other. Both fiber reinforcing materials are laminated on each other in the same thickness. The flange 20b consisting of the nonwoven cloth layer is preformed similarly to the head 20a. After the preformed fiber reinforcing materials of the head 20a and the flange 20b are placed on the male die (lower die), an intermediate die 23 and an upper die 24 are set in position on a cavity 25 in which the fiber reinforcing materials are set. A resin injecting opening 24a communicating with the cavity 25 is formed in the upper die 24 and a resin discharging opening 22b is formed in the lower die 22. After the dies 23 and 24 are set in position, the mixing head of a resin injector is mounted on the resin injecting opening 24a. Then, the die 26 is heated to 70°C and evacuated. Then, RIM cyclopentadiene is injected from the injecting opening 24a similarly to the tennis racket frame so that a polymerization occurs in the die 26. RIM cyclopentadiene is injected for eight seconds at a pressure of 10kg/cm 2 and flow rate of 60cc/sec. Hardening process terminates within one minute after RIM cyclopentadiene is injected. Thus, a helmet as shown in Figs. 8 and 9 is obtained. Pressure may be applied in two stages in the above operation. The primary pressure is set to a low pressure a little lower than 10kg/cm 2 and the secondary pressure may be set to 10kg/cm 2 . Thus, the pressure generated by the flow of resin does not cause fibers arranged in the cavity 25 from dislocating from each other. The above die 26 may be constructed as follows as shown in Fig. 13: Sheet-shaped rubber 28 is provided along a die 27 on which the fiber reinforcing material is provided and a space 29 opposite to the portion in which the fiber reinforcing material is positioned with respect to the rubber 28 communicates with a high pressure supply source (not shown). After the resin is injected, the rubber 28 is pressurized to press the fiber reinforcing material against the surface of the die 27 and discharge extra resin from a resin discharge opening 27a. The above method increases the fiber percentage in the reinforcing material and improves rigidity and shock resistance performance of the baseball helmet. In the second embodiment, woven cloth is used as the fiber reinforcing material which is preformed by placing it along the die. In addition to woven cloth, the following may be used as reinforcing fiber: continuous strand mat shaped by orienting continuous fiber bundles in random directions, chopped strand mat formed by orienting fiber bundles cut to a certain length, and woven filament winding wound around a cylindrical inner ring. Short fiber or a chopped strand mat 30 serving as a fiber reinforcing material may be sprayed on the die 22 together with a fiber binder as a preforming method. Experiment 3 The shock resistance performance of the helmet according to the second embodiment was compared with conventional helmets. Tests were conducted on sample semispherical heads of 220mm in diameter under the condition as shown in Table 1. Penetration tests were conducted using a device as shown in Fig. 16. The test result is shown in Table 2. Tests were conducted as follows: A sample 101 was put on a sample holding tool 100 and a weight 103 having a steel striker 102 at the top end thereof is hung by a hook 104. The weight 103 was dropped to examine whether or not the striker 102 penetrated through the sample 101 and to measure the maximum load and energy required for penetration. The weight of the striker 102 was 12.1kg and its speed was 3.3/sec when it collided with the helmet. Seven kinds of sample helmets were prepared. In Table 1, reference symbols (a), (b), and (c) denote conventional helmets and (d), (e), (f), and (g) denote helmets according to the present invention. (a) Long glass fiber is used as fiber reinforcing material. Unsaturated polyester resin is used as matrix resin. (b) Only ABS is used. (c) Glass continuous strand mat is used as reinforcing fiber. Unsaturated polyester resin is used as matrix resin. (d) Glass-CSM is used as reinforcing fiber. Cyclopentadiene resin is used as matrix resin. (e) Carbon fiber is used as reinforcing fiber. Cyclopentadiene resin is used as matrix resin. (f) Ultra-high-molecular-weight polyethylene fiber is used as reinforcing fiber. Cyclopentadiene resin is used as matrix resin. (g) Aramid resin is used as reinforcing fiber. Cyclopentadiene resin is used as matrix resin. As indicated in Table 2 more energy is required for the striker 102 to penetrate through the helmets of (d) through (g) than for it to penetrate through the conventional helmets (a) through (c). That is, the former are more resistant to a shock than the conventional helmets. Much more energy is required for the striker 102 to penetrate through a helmet comprising ultra-high-molecular-weight polyethylene fiber. Needless to say, the helmet is very resistant to shock. Therefore, the helmet according to the present invention is very effective for protecting the human body. In addition to the tennis racket frame according to the first embodiment and the baseball helmet according to the second embodiment, the present invention is applicable to shock resistant tools including other protecting sporting tools. The present invention can be preferably embodied for plastron 40 of fencing as shown in Fig. 15, face-guard 41 of fencing as shown in Fig. 16, crotch protecting tool 42 such as cup of boxing as shown in Fig. 17, football shoulder protecting tool 43 as shown in Fig. 18, soccer leg leguards as shown in Fig. 19, ear portion 45 of water polo cap as shown in Fig. 20, ice hockey face-guard, ice hockey knee pad, ice hockey elbow pad, ski arm protector or the like. The present invention can also be preferably embodied for a helmet for use in car, on bicycle, in construction work, for infant in play or the like. Further, the present invention is also applicable to shock resistant tools, for preventing breakage, such as pipe 48 for use in bicycle frame as shown in Fig. 21, drop handle 49 of a bicycle as shown in Fig. 22, canoe (not shown) or the like. In addition, the present invention can be used as a face protecting mask in construction work, wall for protecting from machine tool or the like. Tables 3-1, 3-2, 3-3 and 3-4 show conditions in RIM molding (injection pressure, injection period of time, injection flow rate), kind of reinforcing fiber, whether or not nonwoven cloth is provided, method for arranging nonwoven cloth, kind of nonwoven cloth, distribution of reinforcing fiber and nonwoven cloth (design of fiber layer), and content percentage of fiber. As shown in Table 3-1, 3-2, 3-3 and 3-4 in the above-described embodiments, injection pressure is set to less than as low as 20kg/cm 2 and mixing and injections are carried out at a low pressure when fiber density is high. The distribution of nonwoven cloth is as follows: A region which does not require a high strength comprises a nonwoven cloth layer. A region which requires high strength comprises nonwoven cloth layers and reinforcing fiber layers which alternate with each other so as to accelerate the flow of resin. A region which requires a very high strength comprises a reinforcing fiber layer only. Penetration tests were conducted on the above-described shock resistant tools and conventional ones in the same configuration by the same device as shown in Fig. 14. Test results are as shown in Table 4. The constructions of shock resistant tools according to the embodiments of the present invention are as shown in Tables 3-1, 3-2, 3-3 and 3-4 and 4 while those of conventional shock resistant tools are as follows: Plastron of fencing: prepreg formed by impregnating carbon fiber with unhardened epoxy resin was stuck to a die and then heated and pressurized to harden the resin. Fencing face-protecting mask: iron pipe Crotch protecting tool: nylon resin (injection molding) commercially available Football shoulder protecting tool: ultra-high-density polyethylene resin (injection) commercially available Elbow pad and knee pad: ABS resin (injection molding) commercially available Soccer leg guards: nylon resin (injection molding) commer cially available Bicycle frame pipe: epoxy resin reinforced with carbon fiber (interior: urethane foam), handle made of light alloy commercially available Results of shock tests are shown in Table 4. Shock tests were conducted in addition to the penetration test. The fencing plastron was struck with bamboo swords. A shock was felt in the case of the conventional plastron, but a shock was felt to a smaller extent in the case of the plastron according to the embodiment. The weight of conventional fencing face-guard was 1100g while that of the embodiment was 155g. Both face-guard were struck with bamboo swords 500 times. The result is that neither the conventional face-guard nor that of the embodiment was broken. Thus, the shock resistant performance of both face-guards were similar although the face-guard of the embodiment was lighter than the conventional one. The weight of conventional bicycle handle made of light alloy was 290g while the bicycle handle made of light alloy of the embodiment was 210g. The bicycle handle of the embodiment was more operable than the conventional one because the former was lighter than the latter. As apparent from the foregoing description, a shock resistant tool made according to the present invention such as a racket frame or a helmet contains cyclopentadiene resin, having a low melt viscosity, which is used as matrix resin, fiber can be contained in the material of the shock resistant tool at higher percentage. That is, fiber can be contained therein at a desired percentage higher than 40% while according to the conventional method, fiber is contained therein at approximately 30%. Since cyclopentadiene resin is superior in specific strength and specific rigidity, shock resistant performance of shock resistant tool according to the present invention can be outstandingly improved. Shock resistant performance can be improved by using, as reinforcing fiber, continuous fiber or long fiber comprising ultra-high-molecular-weight polyethylene fiber superior in shock resistant performance. In addition, cyclopentadiene resin has a favorable vibration damping performance as well as shock resistant performance. Therefore, a shock resistant tool, for example, a racket frame comprising cyclopentadiene resin is superior in vibration damping characteristic. That is, vibration generated by hitting a ball is transmitted to elbow in a reduced extent. Therefore, the racket frame is preferably used by less powerful players. Since reaction injection molding method is employed, resin injection period of time is less than 10 seconds and the hardening terminates within one minute. Therefore, the molding cycle is very short and productivity is high. Further, fibers provided in the die are not dislocated from each other and fiber can be contained in a predetermined percentage according to a region by setting the balance of flow rate, pressure, and period of time and applying a low injection pressure during the resin injecting operation. In particular, the dislocation of fibers can be effectively prevented by preforming the reinforcing fiber. Resin is capable of flowing smoothly by alternating the reinforcing fiber and nonwoven cloth with each other. The weight of a shock resistant tool can be reduced if a region in which a high strength is not required consists of nonwoven cloth. Hence, manufacturing cost is low.

Claims: A method for manufacturing a shock resistant tool, of fibre re-inforced resin material by reaction injection molding in a die, the fiber reinforced resin material consisting of a resin matrix of cyclopentadiene resin and a reinforcing fibre material containing one of the following reinforcing fibres: ultra-high-molecular-weight polyethylene fiber, carbon fibre, glass fibre, aramid fiber, alumina fibre, silicon carbide fibre, steel fibre, amorphous metal fibre, organic fibre or a combination thereof, the method comprising the steps of : a) preforming the reinforcing fibre material b) placing the preformed reinforcing fibre material in the die in contact with a flexible internal pressure holding member, such as a nylon tube or rubber sheet, c) injecting a reaction mixture for forming said cyclopentadiene resin into the die, and d) applying internal pressure inside the flexible internal pressure holding member to compress the pre-preformed fibre reinforcing material against the surface of the die. A method as claimed in claim 1, wherein said flexible internal pressure holding member is a flexible core which remains in the manufactured shock resistant tool. A method as claimed in claims 1 or 2, wherein the reinforcing fibre material comprises at least one layer of continuous fibre or long fibre and at least one layer of non-voven fibre cloth.

Inventors: KONO MASARU, NAKADE SHINICHI, NIWA KUNIO, YAMAGUCHI TETSUO, KONO, MASARU, NAKADE, SHINICHI, NIWA, KUNIO, YAMAGUCHI, TETSUO
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES LIMITED
Application year: 1991
Main classification: C08J5
IPC codes: A42B3, B29C67, C08J5, B62K19, B29C45, B62K21, B29C70, A63B49, B29K105, A63B33, B29L31