Patent Publication Number: US-2022212844-A1

Title: Hinge cap and hinge cap set

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a hinge cap including an inner lid attached to a container body, a hinge, and an outer lid connected to the inner lid to open and close the cap. The present invention also relates to a hinge cap set including a hinge cap and a packing sheet that is supported inside the hinge cap to enhance the airtightness of the inner lid in the closed state. 
     Description of the Related Art 
     The conventional hinge cap includes a cap body attached to a container body, a hinge portion, and a sealing portion connected to the cap body to open and close the container body (Japan Patent Laid-open Publication No. 2011-246137 A). This hinge cap is configured such that a closed state of the hinge cap is held by engaging a locking portion formed on the cap body and a claw portion formed on the sealing portion. 
     The claw portion is formed by a concave portion and a convex portion formed on an inner surface of a tubular object. In addition, the claw portion is formed on an opposite side of the hinge portion in the circumferential direction of the tubular object. The convex portion of the claw portion is an undercut portion that becomes a mold release resistance when releasing the claw portion from a mold in injection molding. 
     The terms used in the conventional hinge cap, such as the cap body, the sealing portion, the locking portion, and a portion facing the claw portion are referred to, in the present disclosure, as an inner lid, an outer lid, a claw portion, and an engaging portion, respectively. 
     SUMMARY OF THE INVENTION 
     For removing the molded piece with an undercut portion from the mold of the injection molding, 1) a forcible removal from a mold and 2) a slide core in the mold are known. 
     The mold using the technique 2) is more complicated and more expensive than the mold using the technique 1). 
     In the case of the technique 1), when performing forcible removal, the undercut portion is sometimes partially chipped or damaged so that the shape as designed may be deformed to an undesirable shape. In addition, if the engaging portion is formed on the opposite side of the hinge, that is, on a part in the circumferential direction of the tubular object, the mold release resistance is concentrated on the undercut portion of the engaging portion during mold release, and the undercut portion may be easily damaged. If the undercut portion is damaged, the closed state of the hinge cap becomes unstable. 
     The present invention has been created in consideration of the above circumstances, and an object thereof is to provide a hinge cap that makes an engaging portion (an undercut portion), which is a portion of an inner surface of a tubular object that contributes to the stability of a closed state of the hinge cap, less likely to be damaged during mold release in injection molding and stabilizes an engaging state. Another object of the present invention is to provide a hinge cap set capable of improving airtightness using this hinge cap. 
     The present invention presumes an injection-molded hinge cap including: an inner lid attached to a container body; a hinge; and an outer lid connected to the inner lid by the hinge to open and close the cap. 
     The inner lid includes: a tubular inner wall portion that is attached to a mouth portion of the container body; an inner closing plate portion which protrudes from an inner surface of the inner wall portion in a state of closing the inner side thereof and in which a passage port for contents is formed; and a claw portion that protrudes outward in a radial direction from a surface of the inner closing plate portion. 
     The outer lid includes: an outer wall portion having a tubular configuration; an outer closing plate portion protruding from an inner surface of the outer wall portion in a state of closing the inside thereof; and a plurality of convex portions, as undercut portions, and a plurality of concave portions which are arranged side by side in an axial direction on the inner surface of the outer wall portion. 
     One convex portion and a concave portion adjacent to the one convex portion on an inner side of the outer wall portion form an engaging portion which fits to the claw portion in a closed state of the outer lid. A convex portion adjacent to the engaging portion in the axial direction of the outer wall portion (at least one side of the inner side and an open end side) and a concave portion adjacent to the adjacent convex portion on the inner side of the outer wall portion form a mold pressing portion. 
     The engaging portion may include any convex portion of the plurality of convex portions. However, if another convex portion is arranged on the open end side of the outer lid with respect to the engaging portion, the claw portion is likely to come into contact with the another convex portion in an opening/closing operation of the outer lid. The contact corresponds a case where the claw portion is located on a locus of the another convex portion during the opening/closing operation of the outer lid. In such a case, it is difficult to open or close the outer lid unless the claw portion gets over not only the convex portion of the engaging portion but also the another convex portion during the opening/closing operation of the outer lid. In order to enable the outer lid to be opened or closed only by causing the claw portion to get over one convex portion, the following configuration is desirably adopted. 
     That is, the engaging portion includes a convex portion on the most open end side among the plurality of convex portions. If the engaging portion includes the convex portion on the most open end side, the mold pressing portion is adjacent to the engaging portion on the inner side of the outer wall portion. 
     In addition, a row formed by the concave portions and the convex portions of the engaging portion and the mold pressing portion is not limited in number and position with respect to a circumferential direction of the outer wall portion, but the following configuration is desirably adopted when considering the ease of opening and closing the outer lid, the ease of releasing a mold, and the stability of the outer lid in the closed state. 
     That is, the number of the rows formed by the concave portions and the convex portions of the engaging portion and the mold pressing portion is one with respect to the circumferential direction of the outer wall portion, and the row is formed on the opposite side of the hinge. 
     The outer wall portion may or may not include through-holes formed on both sides of the outer wall portion in the circumferential direction with respect to the engaging portion, but the following configuration is desirably adopted in order to stabilize an engaging state between the claw portion and the engaging portion while facilitating the opening/closing operation. 
     That is, the outer wall portion has the through-holes formed on both the sides of the outer wall portion in the circumferential direction with respect to the engaging portion. 
     The through-hole may have any shape, but the following configuration is desirably adopted in order to facilitate the opening/closing operation of the outer lid. 
     That is, the through-hole is an elongated hole extending in the axial direction of the outer wall portion. 
     In the hinge cap, the passage port for the contents may adopt any configuration. The hinge cap may be used alone or used in combination with other parts. However, a hinge cap set in which the hinge cap and a packing sheet are combined desirably adopts the following configuration in order to improve airtightness in a closed state. 
     That is, the hinge cap set includes the hinge cap and the packing sheet that enhances the airtightness in the closed state of the hinge cap. The inner closing plate portion includes: an inner closing plate body protruding inward in the radial direction from the inner surface of the inner wall portion over the whole circumference in a circumferential direction; and a nozzle serving as the passage port for the contents, which is formed on an inner peripheral portion of the inner closing plate body, and protruding from the inner peripheral portion of the inner closing plate body to the opposite side of the container body. The outer lid includes a packing sheet support portion inside. The packing sheet has elasticity to be recessed in a state of being in close contact with a distal end of the nozzle. 
     Note that opening force acts on the outer lid due to restoring force of the packing sheet, and thus, the outer lid is likely to be opened by the restoring force of the packing sheet, for example, unless engaging force between the claw portion and the engaging portion is stronger than that in a hinge cap without the packing sheet. In order to strengthen the engaging force such that the outer lid is not opened by the restoring force of the packing sheet, for example, it is necessary to make a dimension in the radial direction in the engaging state between the claw portion and the engaging portion larger than that in the hinge cap without the packing sheet. Even with such a configuration, a shape of the engaging portion can be brought closer to a shape as designed by the plurality of undercut portions configured to disperse a mold release resistance, and thus, the hinge cap stabilizes the engaging state between the claw portion and the engaging portion, and the packing sheet improves the airtightness. 
     A modification of an embodiment of the invention has the following structure. 
     A hinge cap with a body formed by an injection-molding comprises: a body having an open end with a claw portion provided on a rim of the open end; a hinge provided on the rim at a position opposite to the claw portion; and a lid connected to the body through the hinge to open and close the open end of the body. The lid includes: a tubular outer wall portion; an outer closing plate portion for closing one side of the outer wall portion; and a plurality of convex portions as undercut portions and a plurality of concave portions which are aligned alternately in an axial direction of the tubular outer wall portion on an inner surface of the outer wall portion, one convex portion and a concave portion adjacent to the one convex portion form an engaging portion capable of being engaged with the claw portion in a closed state of the outer lid, and an adjacent convex portion adjacent to the engaging portion and a concave portion adjacent to the adjacent convex portion form a mold pressing portion. 
     In the hinge cap of the present invention, the plurality of convex portions as the undercut portions are arranged side by side in a straight line in the axial direction of the tubular outer wall portion. Thus, the mold release resistance when the outer wall portion is released from the portion of the injection-molding mold that forms the inner surface of the outer wall portion is dispersed to the plurality of undercut portions, and the shape of the engaging portion can be brought closer to a shape as designed, and an engaging state between the engaging portion and the claw portion is stable as compared with, for example, a hinge cap in which one convex portion as an undercut portion is arranged on the outer wall portion. 
     In the hinge cap of the present invention, the claw portion does not have to get over another convex portion during the opening/closing operation of the outer lid when the engaging portion includes the convex portion on the most open end side among the plurality of convex portions so that the opening/closing operation becomes easy. 
     In the hinge cap of the present invention, in a case where the row formed by the concave portions and the convex portions of the engaging portion and the mold pressing portion with respect to the circumferential direction of the outer wall portion is single and formed on the opposite side of the hinge, the outer lid can be easily opened and closed and the mold can be easily removed during injection molding as compared with a case where there are a plurality of the rows, and the closed state of the outer lid is more stable than that in a case where the row is formed in the vicinity of the hinge. 
     In the hinge cap of the present invention, the outer wall portion is easily deformed elastically by the amount of the through-hole when the through-holes are formed on both the sides of the outer wall portion in the circumferential direction with respect to the engaging portion. Thus, the opening/closing operation of the outer lid becomes easy, and the shape of the outer lid does not change by the presence or absence of the through-hole unless external force is applied, so that the engaging state between the claw portion and the engaging portion is stable. 
     In the hinge cap of the present invention, the opening/closing operation of the outer lid becomes easy when the through-hole is the elongated hole extending in the axial direction of the outer wall portion. 
     In the hinge cap set of the present invention, the shape of the engaging portion can be brought closer to the shape as designed by the plurality of undercut portions configured to disperse the mold release resistance, and thus, the engaging state between the claw portion and the mating portion can be held even if the packing sheet has the restoring force, and the airtightness is improved by the close contact between the packing sheet and the nozzle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a top plan view of a hinge cap according to a first embodiment of the present invention formed by an injection-molding. 
         FIG. 1B  is a cross-sectional view taken along a line A-A shown in  FIG. 1A . 
         FIG. 10  is an enlarged view of a portion  10  shown in  FIG. 1B . 
         FIG. 2  is a side view of the hinge cap of  FIG. 1B  viewed from the right. 
         FIG. 3  is a cross-sectional view showing a closed state of the hinge cap to which the packing sheet is attached. 
         FIG. 4A  is a cross-sectional view showing an initial state when an outer wall portion is to be forcibly removed from a mold. 
         FIG. 4B  is a cross-sectional view showing a state immediately after the outer wall portion is forcibly pulled from the mold for separation. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A hinge cap set of a first embodiment of the present invention shown in  FIGS. 1A, 1B, and 10  includes: a hinge cap  1  attached to a container body  100  shown by the dotted line in  FIG. 3 ; and a packing sheet P that enhances airtightness in a closed state of the hinge cap  1  and is supported inside the hinge cap  1 . 
     The hinge cap  1  includes: an inner lid  2  attached to the container body  100 ; two hinged wings  3 ; an outer lid  4  that is connected to the inner lid  2  by the two hinged wings  3  to open and close the cap; and an L-shaped elastic plate  5  that applies opening force and closing force between the inner lid  2  and the outer lid  4 . The hinge cap  1  is made of resin and is formed by an injection-molding, and the inner lid  2 , the hinge  3 , the outer lid  4 , and the elastic plate  5  are configured as an integrated object. An axis of the container body  100 , an axis of the inner lid  2 , and an axis of the outer lid  4  are common in a state in which the container body  100  is assembled with the inner lid  2  and the outer lid  4  is closed by the inner lid  2 . 
     The inner lid  2  includes: a tubular inner wall portion  11  attached to a mouth portion of the container body; an inner closing plate portion  12  having a nozzle  22  protruding from a top surface thereof; and a claw portion  13  protruding outward in a radial direction from the top surface of the inner closing plate portion  12 . 
     Hereinafter, the hinge cap  1  is assumed to be in a state immediately after injection molding. The state immediately after injection molding is a state in which the outer lid  4  is open and the outer lid  4  is arranged on the right side of the inner lid  2  as shown in  FIGS. 1A and 1B . 
     Directions are defined as follows except for the above-described left-right direction. 
     A “container body side” is referred to as the lower side of an object (for example, the inner closing plate portion  12 ) in  FIG. 1B . An “opposite side of the container body” is referred to as the upper side in  FIG. 1B . 
     An “axial direction” of a tubular object is referred to as an up-down direction in  FIG. 1B  in the case of the inner wall portion  11 . 
     A “front-back direction” is referred to as a direction orthogonal to both the up-down direction and the left-right direction. 
     The “radial direction” is referred to as a direction of a straight line that extends radially from a center of a tubular object in a direction perpendicular to the axial direction. 
     As shown in  FIG. 1B , the inner wall portion  11  extends towards the container body side from the inner closing plate portion  12 . In addition, the inner wall portion  11  includes first, second, and third inner wall portions  14 ,  15 , and  16  arranged in said order with intervals in the radial direction. The first, second, and third inner wall portions  14 ,  15 , and  16  are each tubular, more specifically cylindrical, and have a common centerline. That is, the inner wall portions  14 ,  15  and  16  have a common axis. The common axis is also the same as the axis of the container body  100 . The first, second, and third inner wall portions  14 ,  15 , and  16  have one side (lower side) in the axial direction as an open end, and is connected to the inner closing plate portion  12  at the other end (upper side end). The first, second, and third inner wall portions  14 ,  15 , and  16  have longer cylinder lengths in said order, and lower ends thereof terminate at lower levels in said order. 
     The first inner wall portion  14  is arranged inside the mouth portion of the container body  100 . The third inner wall portion  16  covers the second inner wall portion  15  from the outside in the radial direction. A female screw  15   a  is formed on an inner peripheral surface of the second inner wall portion  15 . The female screw  15   a  engages with a male screw formed on an outer peripheral surface of the mouth portion of the container body  100 . 
     The inner closing plate portion  12  includes: an inner closing plate body  21  covering the upper sides of the inner wall portions  14 ,  15  and  16 ; and a nozzle  22  at the center of the inner closing plate body  21  as a passage port for contents in the container body  100 . 
     The nozzle  22  has a tapered shape that protrudes from the inner peripheral portion of the inner closing plate body  21  to the opposite side (upper side) of the container body  100 , and has a shape whose inner and outer diameters decrease toward the upper side. More specifically, the nozzle  22  has the shape of a funnel including a tapered nozzle body portion  23  and a cylindrical discharge port portion  24  protruding upward from a distal end portion of the nozzle body portion  23 . 
     The inner closing plate body  21  is annular, more specifically, toroidal when viewed in a plan view. In addition, the inner closing plate body  21  includes a raised portion  26  in which a portion inside an outer peripheral portion of the surface of the inner closing plate body  21  is raised. When viewed from the top, an outer shape of the raised portion  26  fits to an open end portion of an outer wall portion  31 , which will be described later, of the outer lid  4 . The raised portion  26  includes two semi-circular portions  27  facing each other at opposite sides, one on the side with hinge  3  and the other one on the side away from the hinge  3 , while two parallel linear portions  28  connecting the ends of the two semi-circular portions  27 . Both the two semi-circular portions  27  have a shape that follows the circle which is the outer shape of the inner closing plate body  21 . When the open end portion of the outer wall portion  31  is fitted to the raised portion  26 , the outer wall portion  31  is placed on a portion of the inner closing plate body  21  located outside the raised portion  26  in the radial direction, that is, on the outer peripheral portion of the inner closing plate body  21 . Note that the claw portion  13  protrudes upwardly from the surface of the raised portion  26 . The claw portion  13  will be described in detail later. 
     In addition, an extension wall  29  extending from the inner wall portion  11  (third inner wall portion  16 ) to the other side in the axial direction is formed on the hinge  3  side of the inner closing plate body  21 . 
     The outer lid  4  includes: the tubular outer wall portion  31 ; an outer closing plate portion  32  covering the tubular outer wall portion  31  to close the inside thereof; and a packing sheet support portion  33  on an inner surface of the outer closing plate portion  32 , such that the packing sheet support portion  33  supports a packing sheet P, which will take a tight contact with a distal end of the nozzle  22 ; a plurality of convex portions  34 , serving as mountains or protruding undercut portions on the inner surface of the outer wall portion  31 ; and a plurality of concave portions  35 , serving as valleys or concaved areas between the plurality of convex portions  34  on the inner surface of the outer wall portion  31 . The convex portions  34  and the concave portions  35  are aligned alternately in the direction parallel to the axial direction. 
     The outer closing plate portion  32  includes: an outer closing plate body portion  37  which closes one side of the tubular outer wall portion  31  in the axial direction; and a pedestal portion  38 , which protrudes from an inner surface of the outer closing plate body portion  37 , for placing the packing sheet P. 
     As shown in  FIG. 1A , the pedestal portion  38  is formed in a “cross” shape when viewed from the top. 
     Note that the packing sheet P placed on the pedestal portion  38  has a disk shape, and is a circle having a diameter larger than a dimension of the cross of the pedestal portion  38  in a crossing direction. The packing sheet P is made of a resin that is softer than the hinge cap  1 , and has elasticity enough soft to be slightly recessed when the distal end of the nozzle  22  is pressed, so as to ensure tight contact. 
     The packing sheet support portion  33  includes a pair of support arms  33   a  that hold the packing sheet P in between from opposite sides in a direction that intersects (more specifically, is orthogonal to) with the packing sheet P in the up-down direction. 
     The pair of support arms  33   a  protrude from an inner surface of the outer closing plate portion  32  and extend from the inner surface of the outer wall portion  31  to reach the periphery of the pedestal portion  38 . 
     The support arm  33   a  includes: an arm portion body  33   b  that extends from the hinge  3  side toward the pedestal portion  38  on the inner surface of the outer wall portion  31 ; and a curved support portion body  33   c  that extends in a state of partially covering the periphery of the pedestal portion  38  from a distal end of the arm portion body  33   b  on the pedestal portion  38  side. When viewed from the top, the curved support portion body  33   c  is formed in an arc shape so as to follow an outer shape of the packing sheet P placed on the pedestal portion  38 . In addition, a diameter of the arc formed inside the pair of support portion bodies  33   c  is formed to be slightly smaller than a diameter of the packing sheet P. 
     The outer wall portion  31  has a curved concave surface  31   a , which is concaved in an arc shape when viewed from the side, on its outer surface on the side opposite to the hinge  3 . The curved concave surface  31   a  is formed on the outer closing plate portion  32  side in the axial direction of the outer wall portion  31  to be easily touched by a finger during an operation of opening the outer lid  4 . As shown in  FIG. 2 , the curved concave surface  31   a  includes a rounded upper edge  31   b , left and right side edges  31   c  each extending linearly, and a lower edge  31   d  extending between the side edges  31   c.    
     As shown in  FIG. 1B , the outer wall portion  31  includes a recessed portion  31   v , which is formed by a slope face slanted from the open end (upper end) of the outer wall portion  31  towards the other end, (lower end) at a position adjacent the hinge  3 . A shape of the recessed portion  31   v  corresponds to the shape of the extension wall  29  of the inner lid  2 . In addition, an end on the outer closing plate portion  32  side, which is a closed end (lower end) of the outer wall portion  31 , is formed in a state of being inclined so as to be located on the one side (lower side) in the axial direction as proceeding from the hinge  3  side to the opposite side of the hinge  3 . 
     The outer closing plate body portion  37  has a shape that is inclined so as to be directed to the one side in the axial direction of the outer wall portion  31  as proceeding from the hinge  3  side to the opposite side of the hinge  3  in accordance with the shape of the outer wall portion  31 . In addition, the outer closing plate body portion  37  has a shape that extends to the opposite side of the hinge  3  as compared with a case where the outer wall portion  31  does not have the curved concave surface  31   a , for example. An upper surface of the outer closing plate body portion  37  is inclined to be farther from the inner lid  2  as being separated from the hinge  3  with respect to a plane orthogonal to the axis of the outer lid  4 , that is, the axis that coincides with the common axis in the closed state of the outer lid  4 . The outer closing plate body portion  37  is provided with an eaves portion  31   e  on the opposite side of the side on which the hinge  3  is provided. The eaves portion  31   e  protrudes further outward from an outer tubular surface of the outer wall portion  31 . This facilitates an operation of opening and closing the outer lid  4  in combination with the curved concave surface  31   a.    
     The inner surface of the outer wall portion  31  is formed so as to be larger from the outer closing plate portion  32  side (lower side), which is the one side in the axial direction, to the open end side (upper side), which is the other side in the axial direction in consideration of easy removal of a convex-shaped portion of an injection-molding mold that forms the inner surface of the outer wall portion  31 . That is, the inner surface of the outer wall portion  31  is widened outward in the radial direction as proceeding toward the open end (upward). 
     More specifically, the inner surface of the outer wall portion  31  is a tapered slope except for a part thereof, and is inclined by an angle θ with respect to the up-down direction. Such a part of the inner surface of the outer wall portion  31  is a portion of the inner surface of the outer wall portion  31  corresponding to the curved concave surface  31   a , and includes a slope portion  31   g  that is inclined in a state of being slightly widened to the right side, which is the outer side in the radial direction, as proceeding upward from the outer closing plate portion  32 , and a curved convex surface  31   f  that is curved in a state of being directed to the right side as proceeding upward from an upper end of the slope portion  31   g . An angle of the slope portion  31   g  is smaller than the angle θ of the inner surface of the outer wall portion  31 . The angle θ is preferably 0.2 to 20 degrees. 
     As shown in  FIG. 2 , the outer wall portion  31  is formed with a pair of through-holes  31   h  each penetrating in the radial direction at an interval in the circumferential direction. The pair of through-holes  31   h  are formed in a portion of the whole circumference corresponding to the curved concave surface  31   a , in other words, on the opposite side of the hinge  3  in the circumferential direction. That is, the pair of through-holes  31   h  are elongated holes formed in the outer wall portion  31  and extending in parallel with the axis of the outer lid  4 , extend to both sides of a plurality of convex portions  34   a  and  34   b , which will be described later, and exist so as to sandwich the plurality of convex portions  34   a  and  34   b . Further, the pair of through-holes  31   h  are formed in a range extending over a part of the curved concave surface  31   a.    
     As shown in  FIGS. 1A and 1B , the outer wall portion  31  includes a pair of grooves  31   s , each extending from the open end (upper end) to reach the pair of through-holes  31   h , on the inner surface. Since the groove  31   s  has a bottom and does not penetrate, the open end side of the outer wall portion  31  is an annular shape connected in the circumferential direction. In addition, the groove  31   s  and the through-hole  31   h  are connected in the axial direction (up-down direction) of the outer wall portion  31 . The plurality of convex portions  34  and the plurality of concave portions  35  are arranged between the pair of grooves  31   s  and between the pair of through-holes  31   h  in the circumferential direction of the outer wall portion  31 . 
     As shown in  FIG. 10 , the plurality of convex portions  34  and the plurality of concave portions  35  are arranged alternately side by side in the axial direction of the outer wall portion  31 . The number of rows in which the convex portions  34  and the concave portions  35  are arranged side by side is one in the circumferential direction of the outer wall portion  31 . The concave portion  35  is located closest to the open end side among the plurality of convex portions  34  and the plurality of concave portions  35 . 
     The concave portion  35  is concaved with respect to the inner surface of the outer wall portion  31 . The concave portion  35  is concaved in a stepped manner with respect to the circumferential direction of the outer wall portion  31 . In addition, the number of the concave portions  35  is three in the present embodiment, which are from the open end side, the first concave portion  35   a , the second concave portion  35   b , and the third concave portion  35   c , in  FIG. 10 . The reference sign with a number and an alphabet is used when referring to a particular concave portion, and the reference sign with only a number is used when referring to the concave portions in general. 
     The convex portion  34  protrudes from the inner surface of the outer wall portion  31 , and forms the undercut portion in injection molding. In addition, the number of the convex portions  34  is two in the present embodiment, which are from the open end side, the first convex portion  34   a  and the second convex portion  34   b  in  FIG. 10 . The reference sign with a number and an alphabet is used when referring to a particular convex portion, and the reference sign with only a number is used when referring to the convex portions in general. 
     The concave portion  35   a  on the most open end side among the plurality of concave portions  35 , that is, the first concave portion  35   a  from the open end side, is inclined in a state of being directed outward in the radial direction toward the open end. In addition, the convex portion  34   a  on the most open end side among the plurality of convex portions  34 , that is, the first convex portion  34   a  from the open end side, and the concave portion  35   b  (that is, the second concave portion  35   b  from the open end side) adjacent to the first convex portion  34   a  on the inner side of the outer wall portion  31  form an engaging portion  41  that fits to a distal end portion of the claw portion  13  of the inner lid  2  in the closed state of the outer lid  4 . 
     The claw portion  13  includes: a claw neck portion  13   a  protruding upward from the surface of the raised portion  26  of the inner closing plate portion  12  on the opposite side of the hinge  3 ; and a claw distal end portion  13   b  extending outwardly in the radial direction from an upper end portion of the claw neck portion  13   a.    
     In addition, the convex portion  34   b  adjacent to the engaging portion  41  on the inner side of the outer wall portion  31  is the second convex portion  34   b  from the open end side. The concave portion  35   c  adjacent to the adjacent convex portion  34   b  on the inner side of the outer wall portion  31  is the third concave portion  35   c  from the open end side. The second convex portion  34   b  from the open end side and the third concave portion  35   c  from the open end side each have a shape similar to that of the engaging portion  41 , and form a mold pressing portion  43  that does not fit to the distal end portion of the claw portion  13  in the closed state of the outer lid  4 . In addition, the mold pressing portion  43  is adjacent to the engaging portion  41  on the inner side of the outer wall portion  31 . Note that there is only the first concave portion  35   a  on the open end side of the outer wall portion  31  with respect to the engaging portion  41 , and thus, the mold pressing portion  43  is formed only on the inner side of the outer wall portion  31  with respect to the engaging portion  41  in the present embodiment. The engaging portion  41  and the claw portion  13  constitute an engaging mechanism. 
     In  FIG. 10 , a protrusion amount L 3  of the convex portion  34   b  with respect to the concave portion  35   c  of the mold pressing portion  43  is smaller than a protrusion amount L 1  of the convex portion  34   a  with respect to the concave portion  35   b  in the engaging portion  41  in the present embodiment. Thus, a resistance force received from a mold  50  is smaller in the convex portion  34   a  than in the convex portion  34   b  when forcibly removing the mold  50  as shown in  FIG. 4A , and thus, any damages received from the resistance force is smaller in the convex portion  34   a  than in the convex portion  34   b . In addition, a height H 3  of the convex portion  34   b  from an outer peripheral surface of the outer wall portion  31  is larger than a height H 1  of the convex portion  34   a . Further, a wall thickness (H 1 −L 1 ) of the outer wall portion  31  between the convex portion  34   a  and the convex portion  34   b  is thinner than a wall thickness (H 3 −L 3 ) on the lower side (opposite side of the convex portion  34   a ) from the convex portion  34   b . Thus, the portion with the wall thickness (H 1 −L 1 ) can be easily bent than the portion with the wall thickness (H 3 −L 3 ), as clear from  FIG. 1C . Thus, the resistance force received from the mold  50  can be released by bending at the wall thickness (H 1 −L 1 ) portion when the mold  50  is forcibly removed as shown in  FIG. 4A . Further, the outer wall portion  31  facing the convex portion  34   a  is partially not existing due to the recessed portion  31   v . Thus, the mold  50  can be easily inclined with respect to the outer wall portion  31  toward the recessed portion  31   v  during the removal of the mold  50  forcibly. 
     An engaging slope  41   a  and a pressing slope  43   a , each is slanted with respect to the axial direction of the outer wall portion  31 , are formed on the inner side of each of the convex portion  34   a  of the engaging portion  41  and the convex portion  34   b  of the mold pressing portion  43 , respectively. Both the engaging slope  41   a  and the pressing slope  43   a  are slanted inwardly in the radial direction from the inner side of the outer wall portion  31  to the open end side. In addition, an angle θ 3 , which is an acute angle formed by the pressing slope  43   a  and a straight line in the axial direction, is smaller than an angle θ 1  which is an acute angle formed by the engaging slope  41   a  and a straight line parallel to the axial direction in the present embodiment. Thus, the pressing slope  43   a  is more easy to slip than the engaging slope  41   a  with respect to the mold  50  when the mold  50  is forcibly removed. 
     Note that the engaging portion  41  and the mold pressing portion  43  are arranged on the front side, which is the opposite side of the hinge side where the hinge  3  is located, in the circumferential direction of the outer wall portion  31 . Furthermore, portions  41  and  43  are arranged between the pair of grooves  31   s , and also between the pair of through-holes  31   h . In addition, the engaging portion  41  and the mold pressing portion  43  are arranged in the axial direction of the outer lid  4  to form a single row, and the row exists only one when viewed in the circumferential direction. 
     A reason why the mold pressing portion  43  is provided will be described with reference to  FIGS. 4A and 4B .  FIG. 4A  shows a state in which the outer wall portion  31  and the mold  50  are tightly attached, and the mold  50  is about to be forcibly removed from the outer wall portion  31  by an external force F 0 .  FIG. 4B  shows a state immediately after the forcible removal starts and the outer wall portion  31  is released from the mold  50 . As shown in  FIG. 4A , the external force F 0  is dispersed into action and reaction forces F 1  and F 2  generated at the slope  41   a  and the slope  43   a , where the plurality of undercut portions exist. At the places where the slope  41   a  and the slope  43   a  face the corresponding surfaces of the mold  50 , sliding forces are generated at such slopes. With the dispersion into the forces F 1  and F 2 , a mold release resistance is dispersed, and any damages to the engaging slope  41   a  can be mitigated/prevented. Further, when the outer wall portion  31  is separated from the mold  50  as shown in  FIG. 4B , the recessed portion  31   v  is formed on the hinge side, which is the opposite side of the front side (the side where the engaging portion  41  and the mold pressing portion  43  exist) where the slope  41   a  and the slope  43   a  of the outer wall portion  31  are provided, and thus, the mold  50  can escape while being tilted toward the hinge side, only the pressing slope  43   a  is in contact with the mold  50 , the engaging slope  41   a  can be kept in the state of being separated from the mold  50 , and the engaging slope  41   a  will not be damaged. Even if the engaging slope  41   a  is in contact with the mold  50  immediately after the outer wall portion  31  being separated from the mold  50 , the engaging slope  41   a  can be prevented from being damaged by bending, because the wall thickness of the outer wall portion  31  between the convex portion  34   a  and the convex portion  34   b  is thin. 
     Next, the hinge  3  will be described. The hinge  3  is joined to the outer wall portion  31  of the outer lid  4  and the inner wall portion  11  (third inner wall portion  16 ) of the inner lid  2 , and includes: a first wing  3   a  protruding outward in the radial direction from the outer wall portion  31 ; a second wing  3   b  protruding outward in the radial direction from the inner lid  2 ; and a portion that is joined to the first wing  3   a  and the second wing  3   b  and is thinner than both the first wing  3   a  and the second wing  3   b , that is, a hinge body  3   c  which is a rotation axis portion. The hinge body  3   c  is the center when the outer lid  4  is opened (performs an axis of rotating motion), and thus, is also called the hinge rotation axis  3   c . The elastic plate  5  is located between the pair of hinged wings  3 . In the closed state of the outer lid  4 , as shown in  FIG. 3 , the hinge rotation axis  3   c  is at a level above an upper surface of the inner closing plate portion  12 . As a result, the upper surface of the inner closing plate portion  12  and a lower surface of the outer wall portion  31  can abut on each other reliably and stably as compared with a case where the hinge rotation axis  3   c  is included on the same level as the upper surface of the inner closing plate portion  12 . 
     The elastic plate  5  has a plate shape and functions as a so-called leaf spring. The elastic plate  5  has a cross-sectional shape that is bent in a V shape, and has opposite ends joined, respectively, to the outer wall portion  31  of the outer lid  4  and the inner wall portion  11  of the inner lid  2 . More specifically, the elastic plate  5  includes a first pivotable portion (connected to the inner lid  2  side)  5   a  that is freely bendable, a leaf spring portion  5   c  that has a configuration of a V shape, and a second pivotable portion (connected to the outer lid  4  side)  5   b  that is freely bendable. The first pivotable portion  5   a  and the second pivotable portion  5   b  are thinner than the leaf spring portion  5   c . That is, the thickness of the elastic plate  5  has a tapered thickness that is the thickest in the central portion (leaf spring portion  5   c ) and becomes thinner toward the first and second pivotable portions  5   a  and  5   b . A spring effect is stronger than a plate that has a uniform thickness. Both the first pivotable portion  5   a  and the second pivotable portion  5   b  are located away from the hinge rotation axis  3   c.    
     In the open state of the outer lid  4  as shown in  FIGS. 1B and 1   n  the closed state of the outer lid  4  as shown in  FIG. 3 , the V-shaped leaf spring portion  5  takes such a state that both ends  5   a  and  5   b  are spaced but at a closest possible distance, at which the V-shaped leaf spring portion  5  is in a stable state. As the outer lid  4  rotates about the hinge rotation axis  3   c  by about 180 degrees from the open state ( FIG. 1B ) to the closed state ( FIG. 3 ) or vice versa, the second pivotable portion  5   b  takes a motion of a semi-circle indicated by the dotted line in  FIG. 1B . In a state where the outer lid  4  is rotated about 90 degrees, i.e., a halfway, the V-shaped leaf spring portion  5  opens to take such a state that both ends  5   a  and  5   b  are spaced apart at a furthest possible distance producing a biasing force acting towards the closing/opening direction. When the outer lid  4  passes through a position rotated 90 degrees while operating in the closing direction, the biasing force in the closing direction is applied automatically to complete the closing operation. When the outer lid  4  passes through a position rotated 90 degrees while operating in an opening direction, the biasing force in the opening direction is applied automatically to complete the opening operation. Therefore, the outer lid  4  can be held in the open state or the closed state. The V-shaped leaf spring portion  5  applies snap action to the outer lid  4  in both the opening direction and the closing direction. As a result, the outer lid  4  can be comfortably opened and closed. The above-described engaging mechanism is provided in order to hold the outer lid  4  in the closed state more firmly. 
     In the hinge cap  1  of the first embodiment of the present invention, the two convex portions  34  as the undercut portions are arranged side by side in a straight line in the axial direction of the tubular outer wall portion  31 . Thus, the mold release resistance when the outer wall portion  31  is released from the portion of the injection-molding mold that forms the inner surface of the outer wall portion  31  is dispersed to the plurality of undercut portions. For example, in comparison with a case where a hinge cap has only one convex portion as an undercut portion on the outer wall portion  31 , it is possible to design the shape of the engaging portion  41  freely and nearly the same as a preferred shape as designed. Also, an engaging state between the engaging portion  41  and the claw portion  13  can be made very stable. Moreover, the concave portion  35   b  of the engaging portion  41  has the shape that is concaved with respect to the inner surface of the outer wall portion  31 , and thus, the claw portion  13  is positioned in the circumferential direction with respect to the concave portion  35   b  of the engaging portion  41  in the closed state of the outer lid  4 . Thus, the engaging state between the engaging portion  41  and the claw portion  13  is stable. 
     In the hinge cap  1  of the first embodiment of the present invention, the engaging portion  41  includes the convex portion  34   a  on the most open end side among the plurality of convex portions  34 , and thus, the claw portion  13  does not have to get over another convex portion during the opening/closing operation of the outer lid  4  so that the opening/closing operation becomes smooth. 
     In the hinge cap  1  of the first embodiment of the present invention, there is only one row formed by the concave portions  35  and the convex portions  34  of the engaging portion  41  and the mold pressing portion  43  along the circumferential direction of the outer wall portion  31 . Thus, the outer lid  4  can be easily opened and closed and the mold can be easily removed during injection molding as compared with a case where there are a plurality of the rows. Moreover, the row is formed on the opposite side of the hinge  3 , and thus, the closed state of the outer lid  4  is more stable than that in a case where the row is formed in the vicinity of the hinge  3 . 
     In the hinge cap  1  of the first embodiment of the present invention, the through-holes  31   h  are formed on both sides of the outer wall portion  31  along the circumferential direction with respect to the engaging portion  41 . A portion between the through-holes  31   h  in the outer wall portion  31  can be easily deformed. Thus, the opening/closing operation of the outer lid  4  becomes easy. Also, the shape of the outer lid  4  does not change regardless of the presence or absence of the through-hole  31   h , unless external force is applied. Thus, the engaging state between the claw portion  13  and the engaging portion  41  is stable. That is, since the through-holes  31   h  are formed on both sides of a row of the engaging portion  41  and the mold pressing portion  43  aligned in the axial direction, the row of the engaging portion  41  and the mold pressing portion  43  can be easily displaced outward in the radial direction. Thus, engaging portion  41  can be easily pressed by the claw portion  13 . 
     In the hinge cap  1  of the first embodiment of the present invention, the through-hole  31   h  is the elongated hole extending in the axial direction of the outer wall portion  31 , and thus, the opening/closing operation of the outer lid  4  becomes easier depending on the length of the through-hole  31   h , and the mold release resistance during injection molding also becomes smaller. Moreover, since the through-holes  31   h  as the elongated holes are arranged not only in the engaging portion  41  but also on both the sides of the mold pressing portion  43  in the circumferential direction, the opening/closing operation of the outer lid  4  becomes easy and the mold release resistance becomes small. 
     The hinge cap  1  of the first embodiment of the present invention is provided with the groove  31   s  extending from the open end to the through-hole  31   h  in the inner surface of the outer wall portion  31 , but provided with no cutout portion along the circumferential direction in the open end portion side of the outer wall portion  31 . Thus, the engaging state between the claw portion  13  and the engaging portion  41  is stable even when external force is applied to the outer lid  4 . 
     The hinge cap  1  of the first embodiment of the present invention is provided with the raised portion  26  which is raised from the surface of the inner closing plate portion  12  and is fitted to the open end portion of the outer wall portion  31 , and thus, the closed state of the outer lid  4  is stable. 
     In the hinge cap set of the first embodiment of the present invention, the shape of the engaging portion  41  can be brought closer to the shape as designed by the plurality of undercut portions (convex portions  34 ) configured to disperse the mold release resistance, and thus, the engaging state between the claw portion  13  and the engaging portion  41  can be held even if the packing sheet P has restoring force, and the airtightness is improved by the close contact between the packing sheet P and the nozzle  22 . 
     The present invention is not limited to the above embodiment, and can be appropriately modified within a scope not departing from the spirit thereof. For example, the number of the mold pressing portions  43  is one in the above embodiment, but may be plural without being limited thereto in the present invention. 
     In addition, as compared with the protrusion amount L 1  of the convex portion  34  with respect to the concave portion  35  of the engaging portion  41 , the protrusion amount L 3  of the convex portion  34  with respect to the concave portion  35  of the mold pressing portion  43  is smaller in the above embodiment, but may be desirably equal to or more than, or more desirably larger without being limited thereto in the present invention. As a result, the surface of the engaging portion  41  can be prevented from being damaged as much as possible at the time of mold release, and the engaging state between the engaging portion  41  and the claw portion  13  can be stabilized. 
     In addition, as compared with the angle θ 1  which is the acute angle formed by the engaging slope  41   a  and the straight line parallel to the axial direction, the angle θ 3 , which is the acute angle formed by the pressing slope  43   a  and the straight line parallel to the axial direction, is smaller in the above embodiment, but may be desirably the same, or more desirably larger without being limited thereto in the present invention. As a result, the surface of the engaging portion  41  can be prevented from being damaged as much as possible at the time of mold release, and the engaging state between the engaging portion  41  and the claw portion  13  can be stabilized. 
     Since the mold pressing portion  43  is provided in order to disperse the mold release resistance as described above, the mold release resistance applied to the mold pressing portion  43  increases as the angle θ 3  becomes larger, and the damage to the surface of the engaging portion  41  can be mitigated. As for the angle θ 1  of the engaging portion  41 , the engaging with the claw portion  13  is stronger as the angle is larger, and a click feeling is improved, for example, but the surface of the engaging portion  41  is easily damaged because the resistance at the time of mold release increases. In addition, the mold release resistance itself between the mold  50  and a molded product increases as the angles θ 1  and  83  become larger. Thus, it is necessary to appropriately adjust the respective angles in accordance with the shape of the outer wall portion  31 , which is the molded product, in order to smoothly release the mold  50  from the molded product. It is desirable that an apex  50   b  of the mold  50  (facing the concave portion  35   c ) be equal to or lower than an apex  50   a  of the mold  50  (facing the concave portion  35   b ) when viewed from a central axis of the mold. As a result, the contact of the mold  50  with the engaging slope  41   a  other than the pressing slope  43   a  at the time of releasing the mold  50  is reduced (see  FIG. 4B ), and the damage to the surface of the engaging portion  41  can be prevented. A height of the apex  50   b  is preferably equal to or lower by 0.01 mm than that of the apex  50   a , and more preferably lower by 0.02 to 2 mm than that of the apex  50   a.    
     According to a modification, the hinge cap can be used in a syringe, such as disclosed in Japan Patent Publication No. 2006-61739 which is herein incorporated by reference. In the case of syringe, the nozzle  22 , pedestal portion  38 , packing sheet P, packing sheet support portion  33  are not provided, and thus they can be eliminated. Also, the inner lid  2  is not provided, and the claw portion ( 13 ) is provided directly to a body  100  which can be the syringe cylinder.