Patent Publication Number: US-11040479-B2

Title: Structure and method for manufacturing structure

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. national stage application of International Application No. PCT/JP2016/078931, filed on Sep. 29, 2016, which claims priority to Japanese Patent Application No. 2016-042733, filed on Mar. 4, 2016. The entire contents disclosed in Japanese Patent Application No. 2016-042733 is hereby incorporated herein by reference. 
     BACKGROUND 
     Field of the Invention 
     The present invention relates to a structure and a method for producing a structure. 
     Background Information 
     In recent years, reinforcing members, which are obtained by impregnating reinforcing fibers with resin, for use in automobile parts have attracted attention. More specifically, reinforcing members can be wound around the outer circumference of high-pressure gas storage containers in which hydrogen gas, etc., used as a fuel for automobiles, is stored. Reinforcing members are also used in automobile panels in order to reduce automobile weight. 
     In general, since reinforcing fibers exhibit low adherence to resin, it is necessary to improve the adherence of the reinforcing fibers to resin. 
     In relation to the foregoing, for example, Japanese Laid Open Patent Application No. 61-258065 (Patent Document 1) discloses an adhesiveness improvement method for modifying the surface of an aromatic polyamide fiber and improving the adhesiveness by irradiating plasma on the aromatic polyamide fiber from a direction that is orthogonal to the arrangement surface of the fibers. 
     SUMMARY 
     The stresses to which the above-described high-pressure gas storage containers and automobile panels are subjected differ and are location-dependent. However, product design is based on damage not occurring at locations that receive maximum stress, so that in terms of the overall product, there are locations at which the product thickness is excessive relative to the stress, which increases the weight of the product as a whole. 
     In order to solve the problem described above, the object of the present invention is to provide a structure and a method for producing a structure that can achieve a reduction in weight for the product as a whole by reducing the wall thickness while maintaining suitable strength. 
     A structure according to the present invention which realizes the above-described object comprises a reinforcing member made up of reinforcing fibers that have been impregnated with a resin. The reinforcing member includes a first region formed by irradiating the reinforcing fibers with a plasma, and a second region formed by irradiating the reinforcing fibers with a smaller amount of the plasma or formed without plasma irradiation. The structure is formed by providing with the structure with a reinforcing member such that the first region is positioned in a location that requires more strength than the second region. 
     In addition, a method for producing the structure according to the present invention which realizes the above-described is a method for producing a structure comprising a reinforcing member made of reinforcing fibers impregnated with a resin. In the method for producing the structure, the reinforcing fibers are irradiated with a plasma and impregnated with the resin to form a first region in the reinforcing member. Then, the reinforcing fibers are irradiated with a smaller amount of the plasma than the first region, or plasma is not irradiated thereon, and impregnated with a resin to form a second region in the reinforcing member. Thereafter, the first region is positioned in a location that requires greater strength than the second region. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view illustrating a high-pressure gas storage container according to the present embodiment. 
         FIG. 2  is a view illustrating the state before a reinforcing member is wound around the outer perimeter surface of a liner. 
         FIG. 3  is a view illustrating the state after a reinforcing member is wound around the outer perimeter surface of the liner. 
         FIG. 4  is a cross-sectional view illustrating a portion of a reinforcing member made of reinforcing fibers impregnated with a resin. 
         FIG. 5  is a graph illustrating the distribution of the plasma irradiation amount. 
         FIG. 6  is a graph illustrating the relationship between the stress that is generated in a reinforcing layer and the material strength of the reinforcing layer. 
         FIG. 7  is a view illustrating a device for producing the high-pressure gas storage container. 
         FIG. 8  is a flowchart illustrating a method for producing a high-pressure gas storage container. 
         FIG. 9  is a view illustrating a state in which a reinforcing member is wound around a liner. 
         FIG. 10A  is a view for explaining the effect on a high-pressure gas storage container. 
         FIG. 10B  is a view for explaining the effect on the high-pressure gas storage container. 
         FIG. 10C  is a view for explaining an effect on the high-pressure gas storage container. 
         FIG. 11  is a graph illustrating the relationship between the applied pressure on the high-pressure gas storage container and strain. 
         FIG. 12  is a view illustrating a state in which cracks are generated on the outer perimeter side of a high-pressure gas storage container. 
         FIG. 13  is a graph illustrating the distribution of the plasma irradiation amount according to a first modified example. 
         FIG. 14  is a graph illustrating the distribution of the plasma irradiation amount according to a second modified example. 
         FIG. 15A  is a view for explaining the effect on a high-pressure gas storage container according to a second modified example. 
         FIG. 15B  is a view for explaining an effect on the high-pressure gas storage container according to the second modified example. 
         FIG. 15C  is a view for explaining an effect on the high-pressure gas storage container according to the second modified example. 
         FIG. 16  is a schematic view of an automobile panel. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the present invention will be explained below with reference to the appended drawings. In the explanations of the drawings, the same elements have been assigned the same reference symbols and redundant explanations have been omitted. Dimensional ratios of the drawings are exaggerated for the sake of convenience of explanation and may differ from actual ratios. In the present embodiment, a high-pressure gas storage container  1  formed by winding reinforcing members  20  around the outer perimeter surface  10 A of a liner  10  (corresponding to a core member) will be described as one example of a structure. 
       FIG. 1  is a view illustrating the high-pressure gas storage container  1  according to the present embodiment.  FIG. 2  is a view illustrating the state before the reinforcing members  20  are wound around the outer perimeter surface  10 A of a liner  10 .  FIG. 3  is a view illustrating the state after the reinforcing members  20  are wound around the outer perimeter surface  10 A of the liner  10 .  FIG. 4  is a cross-sectional view illustrating part of the reinforcing member  20  made up of a plurality of reinforcing fibers  21  impregnated with a resin  22 .  FIG. 5  is a graph illustrating the distribution of the irradiation amount of a plasma P.  FIG. 6  is a graph illustrating the relationship between the stress that is generated in a reinforcing layer  30  and the material strength of the reinforcing layer  30 . For ease of comprehension,  FIG. 1  shows a process in which the reinforcing members  20  are wound around the outer perimeter surface  10 A of the liner  10 . In addition, the irradiation of the plasma P and the state of impregnating with the resin  22  are omitted in  FIG. 2 . 
     High-Pressure Gas Storage Container 
     In general, the high-pressure gas storage container  1  according to the present embodiment comprises a liner  10  for holding a high-pressure gas, such as hydrogen gas, and a reinforcing layer  30  that is formed by winding strip-shaped reinforcing members  20  around the outer perimeter surface  10 A of the liner  10 , as is illustrated in  FIGS. 1-3 . 
     In addition, the high-pressure gas storage container  1  is provided with the reinforcing members  20  that are made up of reinforcing fibers  21  that are impregnated with resin  22 , as is illustrated in  FIG. 4 . The reinforcing members  20  include a first region A 1  formed by irradiating the reinforcing fibers  21  with a plasma P and a second region A 2  formed by irradiating the reinforcing fibers  21  with a smaller amount of the plasma P than the first region A 1 , as is illustrated in  FIGS. 2 and 5 . The first region A 1  is positioned on the inner perimeter side of the reinforcing layer  30 , which requires greater strength than the second region A 2 . The configuration of the high-pressure gas storage container  1  according to the present embodiment will be described in detail below. 
     The liner  10  is formed as a tank having the form of a cylinder. The liner  10  has gas barrier properties and suppresses the permeation of high-pressure gas to the outside. The liner  10  comprises a body portion  11  that is centered about the X axis direction, mirror-image portions  12  that are provided at each end of the body portion  11  in the X axis direction, and a mouthpiece  13  that is provided in one of the mirror-image portions  12 , as is illustrated in  FIG. 1 . 
     The body portion  11  is configured with a tubular shape, so as to extend in the X axis direction. 
     The mirror-image portions  12  are curved, so as to taper toward the outside in the X axis direction. 
     The mouthpiece  13  is configured to project from the mirror-image portion  12  outwardly in the X axis direction. A pipe is connected, or a valve mechanism comprising an on-off valve or a pressure reducing valve is connected, to the mouthpiece  13  in order to charge and discharge high-pressure gas into and from the high-pressure gas storage container  1 . The mouthpiece  13  may be provided on the mirror-image portions  12  at each end. 
     A metal or synthetic resin material may be used to constitute the liner  10 . Examples of metals that can be used include iron, aluminum, and stainless steel. Examples of synthetic resins that can be used include polyethylene, polyamide, and polypropylene. 
     The reinforcing layers  30  are formed by winding a predetermined number of the reinforcing members  20  around the outer perimeter surface  10 A of the liner  10  from a winding start end portion  20   a  to a winding termination end portion  20   b  thereof, as is illustrated in  FIGS. 2 and 3 . In the present Specification, the winding start end portion  20   a  means the end portion of a reinforcing member  20  when winding around the outer perimeter surface  10 A of the liner  10  is started, and a winding termination end portion  20   b  means the end portion of the reinforcing member  20  when winding around the outer perimeter surface  10 A of the liner  10  is terminated. 
     The number of times the reinforcing members  20  are wound, that is, the number of reinforcing layers  30 , is not particularly limited, but can be, for example, 20 to 30. By winding the reinforcing members  20  around the outer perimeter surface  10 A of the liner  10 , the reinforcing layers  30  improve the pressure resistance strength of the liner  10 . 
     The reinforcing layer  30  includes a hoop layer  31  that is formed by winding the reinforcing member  20  around the body portion  11  in the circumferential direction and a helical layer  32  formed by winding the reinforcing member  20  around the body portion  11  and the mirror-image portions  12  in a spiral shape, as is illustrated in  FIG. 1 . The hoop layer  31  and the helical layer  32  are stacked in alternating fashion. It is not necessary for the hoop layer  31  and the helical layer  32  to be alternatingly stacked. That is, for example, the reinforcing members  20  can be wound to form two hoop layers  31  followed by two helical layers  32 . 
     Because the hoop layer  31  is formed by winding the reinforcing member  20  around the body portion  11 , the hoop layer contributes to the tensile strength in the radial direction of the body portion  11 . Because the helical layer  32  is formed by winding the reinforcing member  20  around the body portion  11  and the mirror-image portions  12 , the strength in the X axis direction of the high-pressure gas storage container  1  is thereby ensured. 
     The reinforcing members  20  that constitute the reinforcing layer  30  are made up of reinforcing fibers  21  that are impregnated with resin  22 , as is illustrated in  FIG. 4 . 
     The reinforcing fibers  21  according to the present embodiment are formed by irradiating a plasma P thereon. In this manner, by irradiating the plasma P on the reinforcing fibers  21 , it is possible to add an acidic functional group to the reinforcing fibers  21 . As a result, the adhesiveness of the resin  22  to the reinforcing fibers  21  is improved, and the strength imparted by the reinforcing members  20  is improved. 
     In the reinforcing fibers  21 , a relatively large amount of plasma P is irradiated in a first region A 1  on the inner perimeter side of the reinforcing member  20  that constitutes the reinforcing layer  30 , and a relatively small amount of plasma P is irradiated in a second region A 2  on the outer perimeter side of the reinforcing member  20  that constitutes the reinforcing member  30 , as is illustrated in  FIGS. 2 and 5 . More specifically, the reinforcing fibers  21  are formed such that the irradiation amount of the plasma P is continuously gradually reduced from the winding start end portion  20   a  to the winding termination end portion  20   b  of the reinforcing member  20 , as is illustrated in  FIG. 5 . 
     In the reinforcing member  20  made up of reinforcing fibers  21  onto which plasma P has been irradiated in this manner, the strength continuously gradually decreases from the winding start end portion  20   a  to the winding termination end portion  20   b , in the same manner as the distribution of the irradiation amount of the plasma P. 
     Then, the reinforcing member  20  is wound around the outer perimeter surface  10 A of the liner  10  to create a reinforcing layer  30 . At this time, the strength distribution of the reinforcing layer  30  in the radial direction r (refer to  FIG. 3 ) becomes such that the strength decreases from the inner perimeter side to the outer perimeter side in the radial direction r, as is indicated by the solid line in  FIG. 6  (refer to the arrow in  FIG. 6 ). 
     On the other hand, internal pressure acts on the high-pressure gas storage container  1  from the high-pressure gas that is stored inside the liner  10 , which causes stress a to be generated in the reinforcing layer  30 . 
     The stress a that is generated in the reinforcing layer  30  is represented by the following formula (1) at a position R in the radial direction r, where the internal pressure of the high-pressure gas is P, the radius of the reinforcing layer  30  at the outermost perimeter is r2, and the radius of the reinforcing layer  30  at the innermost perimeter is r1, as is illustrated in  FIG. 3 . 
     
       
         
           
             
               
                 
                   
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                           r 
                           1 
                           2 
                         
                       
                       
                         
                           r 
                           2 
                           2 
                         
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                           r 
                           1 
                           2 
                         
                       
                     
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                             r 
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                             R 
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     In this manner, the stress a that is generated in the reinforcing layer  30  continuously gradually decreases from the inner perimeter side to the outer perimeter side, as is indicated by the dotted line in  FIG. 6 . 
     In the present embodiment, the reinforcing member  20  has a strength that can withstand the stress a that is generated in the reinforcing layer  30 , as is illustrated in  FIG. 6 . 
     Examples of reinforcing fibers  21  that can be used to constitute the reinforcing member  20  include carbon fibers, glass fibers, and polyamide fibers. In the present embodiment, carbon fibers, which will be described as an example, have a low coefficient of thermal expansion, excellent dimensional stability, and little reduction in mechanical properties even at high temperatures. Reinforcing fibers  21  are formed in the state of a bundle of about 1,000 to 50,000 carbon fibers. 
     Examples of resins  22  that can be used to constitute the reinforcing member  20  include thermosetting resins and thermoplastic resins. Examples of thermosetting resins that can be used include epoxy resin, polyester resin, and phenol resin. Examples of thermoplastic resins that can be used include polyamide resin and polypropylene resin. 
     Device for Producing the High-Pressure Gas Storage Container 
     Next, a manufacturing device  100  of the high-pressure gas storage container  1  according to the present embodiment will be described with reference to  FIG. 7 .  FIG. 7  is a view illustrating a manufacturing device  100  of a high-pressure gas storage container  1 . 
     The manufacturing device  100  of the high-pressure gas storage container  1  comprises a housing unit  110 , an irradiation unit  120 , an impregnation unit  130 , a transport unit  140 , a detection unit  150 , and a control unit  160 , as is illustrated in  FIG. 7 . 
     The housing unit  110  houses bobbin-shaped reinforcing fibers  21 . The housing portion  110  includes a setting part  111  on which the bobbin-shaped reinforcing fibers  21  are set and four rollers  112 - 115  that maintain the tensile force on the reinforcing fibers  21 . 
     The irradiation unit  120  irradiates a plasma P onto the reinforcing fibers  21 . As the present applicant has disclosed in Japanese Patent Application No. 2014-181512, the irradiation unit  120  preferably irradiates the plasma P from a direction that is tilted from the surface  21 A of the reinforcing fibers  21  in the Y axis direction (direction orthogonal to the surface  21 A). The irradiation unit  120  preferably irradiates the plasma P onto the surface  21 A of the reinforcing fibers  21  from a direction that is tilted at least 30° with respect to the Y axis direction. By irradiating the plasma P from a direction that is tilted with respect to the Y axis direction in this manner, plasma gas is irradiated obliquely onto the surface  21 A of the reinforcing fibers  21 , so that compression of the plasma gas is suppressed, and it is possible to carry out irradiation while allowing the high-temperature portion at the center to be released. Therefore, it is possible to efficiently irradiate plasma P onto the reinforcing fibers  21  and to add an acidic functional group to the reinforcing fibers  21  while reducing damage to the reinforcing fibers  21 . 
     It is preferable to use an AC power source  121  as the power source of the irradiation unit  120 . The AC power source  121  is grounded (grounded). 
     The irradiation intensity of the plasma P that is irradiated from the irradiation unit  120  can be adjusted by adjusting the plasma voltage, current, frequency, electrodes, and gas conditions (composition of the gas). Hereinbelow, “adjusting the irradiation intensity of the plasma P” in the present Specification means adjusting the irradiation intensity of the plasma P by adjusting at least one of the above-described conditions of plasma voltage, current, frequency, electrodes, and gas. 
     One example of the irradiation condition of the plasma P will be described below. 
     From the standpoint of facility in generating the plasma P, the plasma voltage is, for example, 200-400 V, and is preferably 260-280 V. 
     From the standpoint of facility in generating the plasma P, the pulse repetition rate is, for example, 10-30 kHz, and is preferably 16-20 kHz. 
     The plasma irradiation distance is, for example, 2-30 mm, and is preferably 10-15 mm. If the plasma irradiation distance is short, the reinforcing fibers  21  may become damaged, and if the plasma irradiation distance is long, the surface modification effect is reduced. 
     The plasma irradiation time is, for example, 0.1-5.0 seconds, and is preferably 0.5-1.0 second. If the plasma irradiation time is short, the surface modification effect is reduced, and if the plasma irradiation time is long, the reinforcing fibers  21  may become damaged. 
     An example of a plasma gas that can be used is a mixed gas containing 0.5% or more of oxygen, nitrogen, or helium. 
     The impregnation unit  130  impregnates the reinforcing fibers  21  that are irradiated with plasma P with resin  22 . The impregnation unit  130  includes a storage unit  131  in which the resin  22  is stored and a rotation unit  132  that rotates synchronously with the transport of the reinforcing fibers  21  while in contact with the reinforcing fibers  21 , as is illustrated in  FIG. 7 . The impregnation unit  130  further includes an adjustment unit  133  that adjusts the amount of resin  22  that adheres to the rotation unit  132 , and a pair of rollers  134 ,  135  that is provided on the upstream side and the downstream side of the rotation unit  132  in the transport direction and that maintain the tensile force. In addition, the impregnation unit  130  further includes a guide portion  136  that is provided on the downstream side of the downstream side roller  135  and guides the reinforcing fibers  21  toward the liner  10 . 
     The storage unit  131  has a recessed portion  131 A on the top, and the resin  22  is stored in the recessed portion  131 A, as is illustrated in  FIG. 7 . 
     On the lower side, the rotation unit  132  is in contact with the resin  22  that is stored in the recessed portion  131 A, and, on the upper side, the rotation unit rotates while in contact with the reinforcing fibers  21  being transported. The rotation unit  132  rotates clockwise synchronously with the transport of the reinforcing fibers  21 . With the clockwise rotation of the rotation unit  132  in this manner, the resin  22  that adheres to the outer perimeter of the rotation unit  132  is raised and adheres to the reinforcing fibers  21  on which the plasma P has been irradiated. It is thereby possible to impregnate the reinforcing fibers  21  with the resin  22  to form the reinforcing members  20 . The rotation unit  132  maintains the tensile force on the reinforcing fibers  21  on which the plasma P has been irradiated together with the rollers  134 ,  135 . 
     The adjustment unit  133  adjusts the amount of the resin  22  that adheres to the outer perimeter of the rotation unit  132 . The adjustment unit  133  includes a removal part  133 A that removes only a predetermined amount of the resin  22  by coming in contact with the resin  22  that has adhered to the outer perimeter of the rotation unit  132  and a moving part  133 B that moves the removal part  133 A so as to be able to move toward and away from the rotation unit  132 . 
     When the moving part  133 B moves the removal part  133 A to the right side in  FIG. 7 , a larger amount of the resin  22  that has adhered to the outer perimeter of the rotation unit  132  is removed. On the other hand, when the moving part  133 B moves the removal part  133 A to the left side in  FIG. 7 , a smaller amount of the resin  22  that has adhered to the outer perimeter of the rotation unit  132  is removed. 
     The guide portion  136  guides the reinforcing fibers  21  that are impregnated with the resin  22  toward the liner  10 . The guide portion  136  is in the form of an L. 
     The configuration of the impregnation unit  130  is not particularly limited as long as the configuration is capable of impregnating the reinforcing fibers  21  that are irradiated with plasma P with resin  22 . 
     The transport unit  140  winds the reinforcing members  20  that are formed by impregnating, with the resin  22 , the reinforcing fibers  21  on the surface  21 A of which the plasma P has been irradiated, around the outer perimeter surface  10 A of the liner  10 , while transporting the reinforcing fibers  21  from the left side to the right side in  FIG. 7 . The transport unit  140  is a motor. 
     The detection unit  150  detects the transport speed of the reinforcing fibers  21 . A known speed sensor may be used as the detection unit  150 . The location where the detection unit  150  is disposed is not particularly limited as long as the location is within a range in which the reinforcing fibers  21  are transported. 
     The control unit  160  carries out operation control of the irradiation unit  120 , the transport unit  140 , and the like. A control unit configured from a known microcomputer comprising a CPU, a RAM, a ROM, and the like can be used as the control unit  160 . 
     Method for Producing the High-Pressure Gas Storage Container 
     Next, a method for producing the high-pressure gas storage container  1  according to the present embodiment will be described with reference to the flowchart of  FIG. 8 . The method for producing the high-pressure gas storage container  1  according to the present embodiment is carried out according to the filament winding method. 
     First, the transport unit  140  is operated in a state in which the bobbin-shaped reinforcing fibers  21  are set in the setting part  111  and the liner  10  is set in the position shown in  FIG. 7 . The liner  10  thereby rotates and the reinforcing fibers  21  are transported (S 01 ). At this time, the detection unit  150  detects the transport speed of the reinforcing fibers  21 . 
     Next, the irradiation unit  120  irradiates plasma P onto the reinforcing fibers  21  that are being transported (S 02 ). 
     In the step for irradiating the plasma P, the plasma P is irradiated onto the reinforcing fibers  21  that constitute the reinforcing member  20  while the irradiation amount is continuously gradually reduced from the winding start end portion  20   a  to the winding termination end portion  20   b  of the reinforcing member  20  (refer to  FIG. 5 ). 
     The irradiation amount of plasma P is adjusted by adjusting the irradiation intensity of the irradiation unit  120  and the transport speed of the reinforcing fibers  21 . 
     That is, the irradiation amount of the plasma P onto the reinforcing fibers  21  is continuously reduced by carrying out at least one of an adjustment operation to reduce the irradiation intensity of the irradiation unit  120  and an operation to increase the transport speed of the reinforcing fibers  21  from the front end to the rear end in the transport direction. 
     Next, the reinforcing member  20  is formed by impregnating the reinforcing fibers  21  on which the plasma P has been irradiated (S 03 ) with the resin  22 . 
     The strength of the reinforcing member  20  continuously gradually decreases from the winding start end portion  20   a  to the winding termination end portion  20   b , in the same manner as the distribution of the irradiation amount of the plasma P. 
     Next, the reinforcing member  20  is wound around the outer perimeter surface  10 A of the liner  10  to create a reinforcing layer  30  (S 04 ). 
     Because the strength of the reinforcing member  20  continuously gradually decreases from the winding start end portion  20   a  to the winding termination end portion  20   b , a reinforcing layer  30  formed by the winding of the reinforcing member  20  has the strength distribution in the radial direction r indicated by the solid line in  FIG. 6 . 
     In addition, if the liner  10  is rotated at a constant angular velocity co to wind the reinforcing member  20  around the outer perimeter surface  10 A of the liner  10 , the transport speed of the reinforcing fibers  21  changes according to the radius at the time of winding, as is illustrated in  FIG. 9 . Specifically, when the reinforcing member  20  is wound further on the outer perimeter side, the transport speed of the reinforcing fibers  21  is increased. Therefore, the transport speed of the reinforcing fibers  21  increases from the front end to the rear end in the transport direction. Accordingly, the irradiation amount of the plasma P onto the reinforcing fibers  21  is continuously gradually reduced from the winding start end portion  20   a  to the winding termination end portion  20   b  of the reinforcing member  20 . In the present embodiment, in addition to the foregoing, it is preferable to continuously gradually reduce the irradiation amount of the plasma P onto the reinforcing fibers  21  that constitute the reinforcing member  20 , from the winding start end portion  20   a  to the winding termination end portion  20   b , by increasing the angular velocity co, decreasing the irradiation intensity of the irradiation unit  120 , and the like. 
     Next, the effects of the high-pressure gas storage container  1  according to the present embodiment will be described with reference to  FIGS. 10A-12 . 
       FIG. 10A  is a graph illustrating the relationship between the stress that is generated in a reinforcing layer and the material strength of the reinforcing layer when plasma P is not irradiated. 
     Here, a strength design is implemented at the inner perimeter side of the reinforcing layer, where the greatest stress is generated. Therefore, an excessive strength design, corresponding to the area indicated by reference symbol S 1  in  FIG. 10A , is implemented, thereby increasing the weight of the high-pressure gas storage container. 
     In contrast, in the case of a reinforcing layer  30  formed by winding the reinforcing member  20  described above around the outer perimeter surface  10 A of the liner  10 , the strength of the reinforcing layer  30  is enhanced so as to increase from the outer perimeter side toward the inner perimeter side, as is illustrated in  FIG. 10B  (refer to the arrow in  FIG. 10B ). Then, as the strength of the reinforcing layer  30  is enhanced, a margin of strength is accordingly generated on the inner perimeter side in addition to the outer perimeter side. 
     It is then possible to reduce the amount of the reinforcing member  20  that is wound around the outer perimeter surface  10 A of the liner  10  to an extent that does not exceed the strength distribution of the reinforcing layer  30 . As a result, although the stress that is generated in the reinforcing layer  30  increases, as is illustrated in  FIG. 10C , the area indicated by reference symbol S 2  in  FIG. 10C  becomes smaller than the area indicated by the reference symbol S 1  in  FIG. 10A . Thus, the design of excess strength will be relaxed. Therefore, it is possible to reduce the weight of the high-pressure gas storage container  1  by reducing the amount of the reinforcing member  20  that is wound around the liner  10  to reduce the wall thickness of the reinforcing layer  30  while maintaining suitable strength. 
     In addition,  FIG. 11  is a graph illustrating the relationship between pressure that acts on the high-pressure gas storage container and strain. In  FIG. 11 , the horizontal axis represents pressure and the vertical axis represents strain. Additionally, the straight line that includes the rhomboidal plot points in  FIG. 11  illustrates the relationship between the pressure of the high-pressure gas storage container containing reinforcing fibers onto which plasma has not been irradiated and strain. In addition, the straight line that includes the rectangular plot points illustrates the relationship between the pressure of the high-pressure gas storage container  1  according to the present embodiment and strain.  FIG. 11  also shows empirical values for the strain, which were measured with a strain gauge affixed to the outer perimeter side of the reinforcing layer. 
     As is illustrated in  FIG. 11 , it can be seen that the numerical value of the strain is reduced by irradiating plasma P onto the reinforcing fibers  21 . That is, it can be seen that the strength of the reinforcing members  20  is improved by irradiation of the plasma P. 
     In addition, according to the high-pressure gas storage container  1  of the present embodiment, the reinforcing fibers  21  that constitute the reinforcing member  20  are formed such that the irradiation amount of the plasma P is continuously gradually reduced from the winding start end portion  20   a  to the winding termination end portion  20   b  of the reinforcing member  20  with respect to the liner  10 . Thus, it is possible to increase the strength of the inner perimeter side more than the outer perimeter side of the reinforcing layer  30 . Therefore, when an unexpected external force F 1  acts on the high-pressure gas storage container  1  on the outer perimeter side, it is possible to preferentially generate cracks C on the outer perimeter side, as is illustrated in  FIG. 12 . Therefore, it is possible to detect those portions in which cracks have occurred by visual inspection, and thus to improve detectability. 
     In addition, according to the high-pressure gas storage container  1  of the present embodiment, the reinforcing fibers  21  that constitute the reinforcing member  20  are formed such that the irradiation amount of the plasma P is continuously gradually reduced from the winding start end portion  20   a  to the winding termination end portion  20   b  of the reinforcing member  20  with respect to the liner  10 . Therefore, because the strength distribution of the reinforcing member  20  continuously gradually decreases from the winding start end portion  20   a  to the winding termination end portion  20   b , it is possible to suitably suppress the occurrence of shear fractures between the layers  31 ,  32 . 
     As described above, the high-pressure gas storage container  1  according to the present embodiment is a structure comprising a reinforcing member  20  made of reinforcing fibers  21  impregnated with a resin  22 . The reinforcing member  20  includes a first region A 1  formed by irradiating the reinforcing fibers  21  with plasma P, and a second region A 2  formed by irradiating the reinforcing fibers  21  with a smaller amount of the plasma P than the first region A 1 . In addition, the high-pressure gas storage container  1  is formed by providing the container with the reinforcing member  20  such that the first region A 1  is positioned in a location that requires greater strength than the second region A 2 . According to a high-pressure gas storage container  1  configured in this manner, it is possible to add an acidic functional group to the reinforcing fibers  21  by irradiating plasma P on the reinforcing fibers  21 . As a result, the adhesiveness of the resin  22  to the reinforcing fibers  21  is improved, as is the strength of the reinforcing member  20 . Then, the first region A 1  where the strength has been relatively enhanced by irradiating relatively more plasma P is positioned on the inner perimeter side of the reinforcing layer  30 , where strength is required. Therefore, even if the wall thickness is reduced, because the strength has been enhanced by irradiating the plasma P, it is possible to maintain suitable strength. Thus, it is possible achieve a reduction in overall weight by reducing the wall thickness while maintaining suitable strength. 
     In addition, the high-pressure gas storage container  1  further comprises a core member, which is the liner  10 , and the reinforcing member  20  has a strip shape. The strip-shaped reinforcing member  20  is wound around the outer perimeter surface  10 A of the liner  10  to constitute a reinforcing layer  30  made up of a plurality of layers. In the reinforcing layer  30 , the inner perimeter side of the reinforcing layer  30  is constituted by the first region A 1  and the outer perimeter side of the reinforcing layer  30  is constituted from the second region A 2 . According to a structure configured in this manner, it is possible to increase the strength of the inner perimeter side of the reinforcing layer  30 . Therefore, it is possible to reduce the amount of the reinforcing member  20  that is wound, even around a structure onto which high pressure acts on the inner perimeter side of the reinforcing layer  30 , while maintaining suitable strength. Therefore, it is possible achieve a reduction in the overall weight of the product by reducing the wall thickness of the reinforcing layer  30 . 
     Additionally, the core member is a liner  10  that houses high-pressure gas. It is thus possible to reduce the amount of the reinforcing member  20  that is wound around the high-pressure gas storage container  1 , while maintaining suitable strength. Therefore, it is possible achieve a reduction in the overall weight of the product by reducing the wall thickness of the reinforcing layer  30 . 
     In addition, the reinforcing member  20  is formed such that the irradiation amount of the plasma P onto the reinforcing fibers  21  is continuously gradually reduced from the winding start end portion  20   a  to the winding termination end portion  20   b  with respect to the liner  10 . According to this configuration, because the strength of the reinforcing member  20  continuously gradually decreases from the winding start end portion  20   a  to the winding termination end portion  20   b , it is possible to suitably suppress the occurrence of shear fractures between the layers  31 ,  32 . 
     Additionally, as described above, the method for producing a high-pressure gas storage container  1  according to the present embodiment is a method for producing a high-pressure gas storage container  1  comprising a reinforcing member  20  made of reinforcing fibers  21  impregnated with a resin  22 . In the method for producing the high-pressure gas storage container  1 , reinforcing fibers  21  are irradiated with a plasma P and impregnated with a resin  22  to form a first region A 1  in the reinforcing member  20 . The reinforcing fibers  21  are then irradiated with a smaller amount of the plasma P than the first region A 1  and impregnated with a resin  22  to form a second region A 2  of the reinforcing member  20 . The first region A 1  is then positioned in a location that requires greater strength than the second region A 2 . According to this production method, it is possible to add an acidic functional group to the reinforcing fibers  21  by irradiating plasma P onto the reinforcing fibers  21 . As a result, the adhesiveness of the resin  22  to the reinforcing fibers  21  is improved, as is the strength of the reinforcing member  20 . Then, the first region A 1  where the strength has been relatively enhanced by irradiating relatively more plasma P is positioned on the inner perimeter side of the reinforcing layer  30 , where strength is required. Therefore, even if the wall thickness is reduced, because the strength has been enhanced by irradiation of the plasma P, it is possible to maintain suitable strength. Thus, it is possible to provide a high-pressure gas storage container  1  that can realize a reduction in overall weight by reducing the wall thickness while maintaining a suitable strength. 
     Additionally, that reinforcing fibers  21  that are formed in a strip shape are transported and the reinforcing fibers  21  are irradiated with plasma P on the front end in the transport direction and impregnated with a resin  22  to form a first region A 1  in the reinforcing member  20 . In addition, the reinforcing fibers  21  are irradiated with a smaller amount of the plasma P than the first region A 1  on the rear end in the transport direction and impregnated with a resin  22  to form a second region A 2  in the reinforcing member  20 . The reinforcing member  20  in which the first region A 1  and the second region A 2  have been formed is then wound around the core member, which is the liner  10 . According to this production method, it is possible to increase the strength of the inner perimeter side of the reinforcing layer  30 . Therefore, it is possible to reduce the amount of the reinforcing member  20  that is wound, even around a structure onto which high pressure acts on the inner perimeter side of the reinforcing layer  30 , while maintaining a suitable strength. Therefore, it is possible achieve a reduction in the overall weight of the product by reducing the wall thickness of the reinforcing layer  30 . 
     In addition, the core member is a liner  10  that houses high-pressure gas. Accordingly, it is possible to reduce the amount of the reinforcing member  20  that is wound around the high-pressure gas storage container  1  while maintaining a suitable strength. Therefore, it is possible achieve an overall reduction in weight of the product by reducing the wall thickness of the reinforcing layer  30 . 
     In addition, the plasma P is irradiated, as the irradiated amount is continuously gradually reduced, onto the reinforcing fibers  21 , from the winding start end portion  20   a  to the winding termination end portion  20   b  of the reinforcing member  20  with respect to the liner  10 . According to this production method, it is possible to produce a high-pressure gas storage container in which the strength of the reinforcing member  20  continuously gradually decreases from the winding start end portion  20   a  to the winding termination end portion  20   b . Accordingly, it is possible to suitably suppress the occurrence of shear fractures between the layers  31  and  32 . 
     In addition, the irradiation amount of the plasma P is adjusted by adjusting at least one of the plasma voltage, current, frequency, electrodes, and gas conditions to adjust the irradiation intensity of the plasma P. According to this production method, it is possible to easily adjust the irradiation amount of the plasma P with respect to the reinforcing fibers  21 . Therefore, it is possible to adjust the strength of the reinforcing member  20  such that the area indicated by the reference symbol S 2  in  FIG. 10C  is reduced. In this manner, the design of excess strength can be further relaxed by reduction of the area indicated by the reference symbol S 2 . 
     Additionally, the irradiation amount of the plasma P can be adjusted by changing the transport speed of the reinforcing fibers  21  during irradiation of plasma P onto the reinforcing fibers  21 . According to this production method, it is possible to increase the transport speed of the reinforcing fibers  21  during irradiation of plasma P onto the reinforcing fibers  21  on the outer perimeter side of the reinforcing layer  30 , where the irradiation amount of the plasma P onto the reinforcing fibers  21  is low. Therefore, it is possible to reduce the manufacturing time and to enhance productivity. 
     Additionally, the plasma P is irradiated onto the surface  21 A of the reinforcing fibers  21  from a direction that is tilted from the Y axis direction that is orthogonal to the surface  21 A. According to this production method, because the plasma gas is irradiated from a direction that is tilted from the surface  21 A of the reinforcing fibers  21 , compression of the plasma gas is suppressed, and it is possible to carry out irradiation while allowing the high-temperature portion at the center to be released. Therefore, it is possible to efficiently irradiate plasma P onto the reinforcing fibers  21  and to add an acidic functional group to the reinforcing fibers  21  while reducing damage to the reinforcing fibers  21 . 
     First Modified Example 
     A first modified example of the above-described embodiment will be described below. 
     A high-pressure gas storage container according to the first modified example is different from the high-pressure gas storage container  1  according to the embodiment described above in the distribution of the irradiation amount of the plasma P onto the reinforcing fibers  21 . 
       FIG. 13  is a graph illustrating a distribution of the irradiation amount of the plasma P according to the first modified example. 
     The reinforcing fibers  21  of the high-pressure gas storage container according to the first modified example are formed such that the irradiation amount of the plasma P is gradually reduced in stepwise fashion from the winding start end portion  20   a  to the winding termination end portion  20   b  of the reinforcing member  20  with respect to the liner  10 , as is illustrated in  FIG. 13 . 
     More specifically, a set amount of plasma P is irradiated onto a hoop layer  31   a , as is illustrated in  FIG. 13 . Additionally, plasma P in a smaller amount than in the hoop layer  31   a  is irradiated onto an adjacent helical layer  32  on the outer perimeter side of the hoop layer  31   a . Furthermore, plasma P in a smaller amount than in the helical layer  32  is irradiated onto an adjacent hoop layer  31   b  on the outer perimeter side of the helical layer  32 . Thereafter, the irradiation amount of the plasma P is gradually reduced in stepwise fashion toward the outer perimeter side, in the order of helical layer  32  and hoop layer  31 . 
     In a reinforcing member  20  made up of reinforcing fibers  21  onto which plasma P has been irradiated in this manner, the strength continuously gradually decreases from the winding start end portion  20   a  to the winding termination end portion  20   b , in the same manner as the distribution of the irradiation amount of the plasma P. 
     Then, if such a reinforcing member  20  is wound around the outer perimeter surface  10 A of the liner  10  to form a reinforcing layer  30 , the strength distribution along the radial direction r of the reinforcing layer  30  decreases from the inner perimeter side to the outer perimeter side in the radial direction r, in the same manner as the strength distribution of the reinforcing layer  30  according to the embodiment described above. 
     Next, a method for producing the high-pressure gas storage container according to the first modified example will be described. 
     Here, only the step for irradiating plasma P will be described. 
     In the step for irradiating the plasma P, the plasma P is irradiated, while the irradiated amount is gradually reduced in stepwise fashion, onto the reinforcing fibers  21  that constitute the reinforcing member  20 , from the winding start end portion  20   a  to the winding termination end portion  20   b  of the reinforcing member  20  with respect to the liner  10 . The step for irradiating the plasma P will be described in detail below. 
     The step for irradiating plasma P includes a first irradiation step for irradiating a set amount of the plasma P onto the reinforcing fibers  21  that constitute the reinforcing member  20  that is wound in/the hoop layer  31 , Additionally, the step for irradiating plasma P includes a second irradiation step for irradiating a set amount of the plasma P onto the reinforcing fibers  21  that constitute the reinforcing member  20  that is wound in the helical layer  32 . 
     The first irradiation step and the second irradiation step are carried out in alternating fashion, and the irradiation amount of the plasma P is reduced when switching from the first irradiation step to the second irradiation step, and when switching from the second irradiation step to the first irradiation step. 
     As described above, in the high-pressure gas storage container according to the first modified example, the reinforcing member  20  is formed such that the irradiation amount of the plasma P onto the reinforcing fibers  21  is gradually reduced in stepwise fashion from the winding start end portion  20   a  to the winding termination end portion  20   b  with respect to the liner  10 . According to a high-pressure gas storage container configured in this manner, it is possible to increase the strength of the inner perimeter side of the reinforcing layer  30 . Therefore, it is possible to reduce the amount of the reinforcing member  20  that is wound, even around a high-pressure gas storage container on which high pressure acts on the inner perimeter side of the reinforcing layer  30 , while maintaining a suitable strength. Therefore, it is possible achieve an overall reduction in weight of the product by reducing the wall thickness of the reinforcing layer  30 . 
     Additionally, the reinforcing layer  30  is formed such that the irradiation amount of the plasma P onto the reinforcing fibers  21  is gradually reduced in stepwise fashion for each layer  31 ,  32 . Accordingly, the irradiation amount of the plasma P in one layer  31 ,  32  becomes constant. Therefore, because the strength of the reinforcing layer  30  in one layer  31 ,  32  can be made constant, it is possible to provide a high-pressure gas storage container having a favorable strength distribution. 
     Additionally, in the method for producing a high-pressure gas storage container according to the first modified example, the plasma P is irradiated, while the irradiated amount is gradually reduced in stepwise fashion, onto the reinforcing fibers  21  from the winding start end portion  20   a  to the winding termination end portion  20   b  of the reinforcing member  20  with respect to the liner  10 . According to this production method, it is possible to produce a high-pressure gas storage container in which the strength of the inner perimeter side of the reinforcing layer  30  is high. Therefore, it is possible to reduce the amount of the reinforcing member  20  that is wound, even around a high-pressure gas storage container on which high pressure acts at the inner perimeter side, while maintaining a suitable strength. Therefore, it is possible achieve an overall reduction in weight of the product by reducing the wall thickness of the reinforcing layer  30 . 
     In addition, when plasma P is irradiated onto the reinforcing fibers  21 , the irradiation amount of the plasma P is reduced when the irradiation target of the plasma P switches from the reinforcing fibers  21  in one layer to the reinforcing fibers  21  in another adjacent layer on the outer perimeter side. According to this production method, the irradiation amount of the plasma P in one layer  31 ,  32  becomes constant. Therefore, because the strength of the reinforcing layer  30  in one layer  31 ,  32  can be made constant, it is possible to provide a high-pressure gas storage container having a favorable strength distribution. 
     Second Modified Example 
     A second modified example of the above-described embodiment will be described below. 
     A high-pressure gas storage container according to the second modified example is different from the high-pressure gas storage container  1  according to the embodiment described above in the distribution of the irradiation amount of the plasma P onto the reinforcing fibers  21 . 
       FIG. 14  is a graph illustrating the distribution of the irradiation amount of the plasma P according to a second modified example. 
     In the second modified example, a set amount of the plasma P is irradiated onto the reinforcing fibers  21  that constitute the reinforcing member  20  from the winding start end portion  20   a  to an intermediate portion  20   c  (refer to  FIG. 2 ) positioned between the winding start end portion  20   a  and the winding termination end portion  20   b , as is illustrated in  FIG. 14 . In addition, plasma P is not irradiated onto the reinforcing fibers  21  that constitute the reinforcing member  20  from the intermediate portion  20   c  to the winding termination end portion  20   b.    
     A reinforcing member made up of reinforcing fibers  21  onto which plasma P has been irradiated in this manner has a strength distribution in which the strength increases only from the winding start end portion  20   a  to the intermediate portion  20   c , in the same manner as the distribution of the irradiation amount of the plasma P. 
     Next, a method for producing the high-pressure gas storage container according to the second modified example will be described. 
     Here, only the step for irradiating the plasma P will be described. 
     In the step for irradiating the plasma P, a set amount of the plasma P is irradiated onto the reinforcing fibers  21  that constitute the reinforcing member  20  from the winding start end portion  20   a  to the intermediate portion  20   c . Thereafter, irradiation of the plasma P is stopped. That is, plasma P is not irradiated onto the reinforcing fibers  21  that constitute the reinforcing member  20  from the intermediate portion  20   c  to the winding termination end portion  20   b.    
     Next, the effects of the high-pressure gas storage container according to the second modified example will be described with reference to  FIGS. 15A-15C . 
       FIG. 15A  is a graph illustrating the relationship between the stress that is generated in a reinforcing layer and the material strength of the reinforcing layer when plasma P is not irradiated. 
     Here, as was described above, strength design is implemented at the inner perimeter side of the reinforcing layer, where the greatest stress is generated. Therefore, an excessive strength design, corresponding to the area indicated by reference symbol S 1  in  FIG. 15A , is implemented, thereby increasing the weight of the high-pressure gas storage container. 
     In contrast, in the case of a reinforcing layer  30  formed by winding the reinforcing member  20  according to the second modified example around the outer perimeter surface  10 A of the liner  10 , the strength of the inner perimeter side of the reinforcing layer  30  is enhanced, as is illustrated in  FIG. 15B  (refer to the arrow in  FIG. 15B ). Then, as the strength of the inner perimeter side of the reinforcing layer  30  is enhanced, a margin of strength is accordingly generated on the inner perimeter side in addition to the outer perimeter side. 
     It is then possible to reduce the amount of the reinforcing member  20  that is wound around the outer perimeter surface  10 A of the liner  10  to an extent that does not exceed the strength distribution of the reinforcing layer  30 . As a result, although the stress that is generated in the reinforcing layer  30  increases, as is illustrated in  FIG. 15C , the area indicated by reference symbol S 3  in  FIG. 15C  becomes smaller than the area indicated by the reference symbol S 1  in  FIG. 15A . Accordingly, the design of excess strength can be relaxed. Therefore, it is possible to reduce the weight of the high-pressure gas storage container by reducing the amount of the reinforcing member  20  that is wound around the liner  10  to reduce the wall thickness of the reinforcing layer  30  while maintaining a suitable strength. 
     As described above, in the high-pressure gas storage container according to the second modified example, the reinforcing member  20  from the winding start end portion  20   a  to the intermediate portion  20   c  is formed such that a set amount of the plasma P is irradiated onto the reinforcing fibers  21 . Also, in the reinforcing member  20  from the intermediate portion  20   c  to the winding termination end portion  20   b , plasma P is not irradiated onto the reinforcing fibers  21 . When such a reinforcing member  20  is produced, the irradiation of the plasma P may be stopped at the intermediate portion  20   c . Therefore, it is possible to easily produce the high-pressure gas storage container. 
     In addition, as described above, in the method for producing a high-pressure gas storage container according to the second modified example, a set amount of plasma P is irradiated onto the reinforcing fibers  21  that constitute the reinforcing member  20  from the winding start end portion  20   a  to the intermediate portion  20   c . Also, plasma P is not irradiated onto the reinforcing fibers  21  that constitute the reinforcing member  20  from the intermediate portion  20   c  to the winding termination end portion  20   b . According to this production method, because it suffices to stop the irradiation of the plasma P at the intermediate portion  20   c , it is possible to easily produce a high-pressure gas storage container. 
     The present invention is not limited to the embodiment and modified example described above, and various modifications are possible within the scope of the claims. 
     In the above-described embodiment, the first modified example, and the second modified example, a high-pressure gas storage container formed by winding a reinforcing member  20  around the outer perimeter surface  10 A of a liner  10  was described as an example of a structure. However, the invention may be applied to an automobile panel  5  as a structure, such as that shown in  FIG. 16 . An automobile panel  5  is formed in the form of a panel with a reinforcing member  20  as the core member. The panel  5  is formed according to the RTM (Resin Transfer Molding) method. For example, in the case that an external force F 2  shown in  FIG. 16  acts on the panel  5 , a first region A 1  where the strength has been relatively enhanced by irradiating relatively more plasma P is positioned at the periphery of the portion on which the external force F 2  acts. As a result, even if the wall thickness is reduced, because the strength has been enhanced by irradiating the plasma P, it is possible to maintain a suitable strength. Accordingly, it is possible to provide a panel  5  for which an overall reduction in weight can be achieved by reducing the wall thickness while maintaining suitable strength. 
     Additionally, in the embodiment described above, the irradiation intensity of the plasma P is adjusted by adjusting the plasma voltage, current, frequency, electrodes, and gas conditions. However, the irradiation intensity of the plasma P may be adjusted by providing a filter between the irradiation unit  120  and the reinforcing fibers  21 . With this configuration, it is possible easily to adjust amount of the plasma P irradiated onto the reinforcing fibers  21  without manipulating the plasma voltage, current, frequency, electrode, and gas conditions. 
     In addition, in the above-described embodiment, the liner  10  is cylindrical in shape, but it may have the form of a rectangular parallelepiped or the like.