JP2018038813A - Plunger for syringe, manufacturing method thereof, and medical syringe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plunger for syringes uniformizing a degree of welding at a contact surface between a gasket and a plunger body, and capable of preventing detachment of both, and an occurrence of shape deformation due to positional deviation and distortion of the gasket when fitting the plunger body to the gasket, and a manufacturing method thereof and a medical syringe.SOLUTION: A plunger 21 for syringes according to the present invention includes: a plunger body 20; a connecting part 24 provided at a tip of the plunger body 20; and a gasket 23 whose tip end is closed and rear end is opened, and that stores at least a part of the connecting part 24 from the rear end side. The connecting part 24 includes a recessed portion 27 at a center of a tip end surface thereof, where the recessed portion 27 is a molten resin receiving portion that receives a molten resin for forming the gasket to be supplied when molding the gasket 23. An inner wall surface of the gasket 23 is welded with the connecting part 24, at a contact surface including at least the recessed portion 27.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a plunger for a syringe, a method for manufacturing the same, and a medical syringe, and more specifically, a plunger for a syringe capable of preventing the occurrence of displacement and shape deformation of a gasket, a method for manufacturing the same, and a medical syringe. About.

  In recent years, many prefilled syringes filled with a chemical solution in advance have been used. Gasket insertion in a prefilled syringe is performed by filling the outer cylinder with the sealed end opening filled with chemicals, placing the gasket in the opening of the outer cylinder under a reduced pressure atmosphere (vacuum atmosphere), and then normal pressure A so-called vacuum plugging method is used in which the gasket is inserted into the outer cylinder by setting the state. In addition, the prefilled syringe may be assembled by attaching a plunger to the gasket after the gasket is plugged. In such an embodiment, the plunger can be easily attached to the gasket, and at the time of installation. In order to prevent liquid leakage and to suppress an increase in internal pressure, it is common to provide a male threaded portion on the plunger and a female threaded portion on the gasket and to connect them by screwing (for example, the following patent document) 1).

  However, if the plunger and the gasket are connected by screwing, they may loosen during assembly or use, and the plunger may be detached. Further, when connecting the plunger to the gasket, it is necessary to screw the plunger into the outer cylinder for syringe while rotating the plunger. However, if the plunger is pushed without rotating, it is difficult to screw the gasket. As a result, the gasket that has been previously plugged may be pressed by the plunger, and shape deformation such as displacement or distortion of the gasket may occur. Thereby, there exists a problem that the liquid leakage of the chemical | medical solution with which it fills in the outer cylinder for syringes, or mixing of a bubble generate | occur | produces.

  Further, in Patent Document 2 below, a plunger main body part corresponding to a female screw part is provided inside a piston main body corresponding to a gasket, and screwed with a second part of the plunger main body corresponding to a male screw part. A plunger of a medical syringe to be connected by making it be disclosed is disclosed. According to the said patent document, the piston main body and the component of the plunger main-body part have the structure welded mutually in the contact surface.

  However, in Patent Document 2, no consideration is given to uniformly performing the degree of welding on the contact surface between the piston body and the parts of the plunger body. Therefore, for example, when sterilizing with an autoclave or the like performed before and after filling with a chemical solution, there is a problem that the piston main body and the plunger main body parts are detached from the welded contact surface. Further, if the degree of welding is not uniform, the smoothness of the tip surface of the piston main body is impaired due to this, and there is also a problem that unevenness occurs. When irregularities occur on the tip surface of the piston body, it becomes difficult to discharge the chemical without filling the syringe.

  Furthermore, when the medical syringe is installed in a position higher than the patient while the medical syringe is filled with the medical solution, the medical solution will flow rapidly toward the patient due to the pressure difference due to the height difference. The so-called siphoning phenomenon may occur. Therefore, in general, the plunger main body is fixed to the syringe pump device to prevent the occurrence of the siphoning phenomenon. However, as described above, the degree of welding on the contact surface between the piston main body and the plunger main body parts. Is non-uniform, even if the plunger body is fixed, as a result of the piston body being detached from the plunger body parts, a siphoning phenomenon occurs, and the drug solution flows rapidly toward the patient. There's a problem. In addition, there is also a problem that the piston body is detached from the parts of the plunger body even in the case of reverse blood performed to confirm that the patient is properly punctured.

JP 2003-159330 A JP-T-2006-502896

  The present invention has been made in view of the above-mentioned problems, and its purpose is that the degree of welding on the contact surface between the gasket and the plunger main body is uniform, and when both are detached and the plunger main body is attached to the gasket. It is providing the plunger for syringes which can prevent generation | occurrence | production of the shape deformation by position shift and distortion of the gasket of this, its manufacturing method, and a medical syringe.

  In order to solve the above-mentioned conventional problems, the inventors of the present application examined a syringe plunger, a manufacturing method thereof, and a medical syringe. As a result, the inventors have found that the object can be achieved by adopting the following configuration, and have completed the present invention.

  That is, in order to solve the above problems, the plunger for a syringe according to the present invention has a plunger main body, a connection portion provided at the tip of the plunger main body, the tip closed, and the rear end In the syringe plunger provided with an opened gasket and containing at least a part of the connection portion from the rear end side, a concave portion is provided at the center of the tip surface of the connection portion, The recessed portion is a molten resin receiving portion for receiving a molten resin for forming a gasket supplied at the time of forming the gasket, and the gasket is welded to the connecting portion and a contact surface including at least the recessed portion. It is characterized by that.

  According to the said structure, the plunger main-body part and the gasket are connected via the connection part. That is, when the connecting portion is provided at the tip of the plunger main body and the gasket accommodates at least a part of the connecting portion from the opened rear end side, the syringe plunger (hereinafter referred to as “plunger”) There is.) The gasket is welded on the contact surface with the connecting portion, and has an integral structure. A concave portion is provided at the center of the front end surface of the connecting portion, and the concave portion is also in contact with and welded to the inner wall surface of the gasket. The concave portion functions as a molten resin receiving portion for receiving a molten resin for forming a gasket supplied at the time of forming the gasket. Therefore, for example, when molten resin is supplied into the cavity for molding the gasket from a position facing the recess, the molten resin first flows into the recess with respect to the connecting portion, and then spreads and fills the entire cavity. . By controlling the flow state of the molten resin in this way, it is possible to improve the degree of welding at the contact surface between the gasket and the connecting portion from becoming non-uniform.

  In addition, the plunger of the said structure does not connect a plunger directly to the said gasket by the screw structure etc. like the conventional plunger and a gasket. Since the gasket is structured to be connected to the plunger main body through a connection portion welded on the contact surface, the assembly work for directly connecting the plunger to the gasket can be omitted. It is possible to prevent the occurrence of shape deformation due to gasket misalignment or distortion.

  In the above configuration, it is preferable that a plurality of groove portions are provided radially or spirally around the concave portion on the front end surface of the connection portion. For example, the molten resin supplied from a position facing the concave portion first flows into the concave portion, then flows through a groove portion provided radially or spirally around the concave portion, and spreads over the entire cavity. In this way, by guiding the flow direction of the molten resin, it is possible to further improve the non-uniform degree of welding on the contact surface between the gasket and the connecting portion.

  Further, in the above configuration, a flange portion projecting radially outward is provided on a side of the connection portion that is connected to the plunger main body portion, and the diameter of the flange portion is the outer periphery of the gasket. It is preferable that the diameter of the surface is substantially the same. By providing a flange portion having substantially the same diameter as the diameter of the outer peripheral surface of the gasket in the connecting portion, when the plunger for syringe of the present invention is accommodated in the outer cylinder of the syringe and combined, the inner periphery of the syringe The surface can be slid with the flange portion in contact therewith. As a result, the syringe plunger of the present invention can be prevented from sliding while swinging, and the sliding performance of the syringe plunger relative to the syringe can be improved.

  In the above-described configuration, the connection portion includes a female screw portion therein, and the plunger main body portion includes a male screw portion screwed into the female screw portion, and the connection portion and the plunger main body portion. Are preferably joined by a screwed structure. In the present invention, unlike the conventional plunger and gasket, the plunger is not directly connected to the gasket by a screw structure or the like. The plunger main body is joined by screwing to a connecting portion that is at least partially housed in the gasket and integrally provided by welding. That is, since the gasket is integrally formed with the connecting portion, even if the male screw portion of the plunger main body portion is connected to the female screw portion of the connecting portion by screwing, the displacement of the gasket or It is possible to prevent distortion and shape deformation. As a result, it is possible to prevent liquid leakage of chemicals and mixing of bubbles due to these.

  In the above configuration, the connection portion has a main body portion provided with an annular step portion and a top portion provided at a tip of the main body portion, and the female screw portion is a position where the step portion is formed in the main body portion. It is provided on the rear end side, and the inside of the connection part is hollow on the top side than the step part by joining with the plunger main body part by a screwing structure with the connection part. Also good.

  In the above configuration, the gasket is preferably made of a thermoplastic elastomer resin.

  Moreover, in order to solve the above-mentioned problem, the manufacturing method of the plunger for a syringe according to the present invention includes a plunger main body, a connecting portion provided at a tip of the plunger main body, and a tip closed. In the manufacturing method of the plunger for a syringe provided with a gasket having an open rear end and containing at least a part of the connection portion from the rear end side, a tip shape and a side shape of the connection portion are formed. Forming the connecting portion having a concave portion at the center of the tip surface using a first mold having an inner shape for forming a common die having an inner shape for forming the inner shape of the connecting portion And a step of forming a cavity for molding the gasket when combined with the common mold, and in a position facing the concave portion in the connection portion, the molten resin toward the concave portion. Using a second mold having a molten resin supply gate to supply, the mold is closed with the common mold while the connection portion is held inside, and the molten resin is supplied from the molten resin supply gate, and the cavity It has a step of forming the gasket welded on the contact surface including at least the concave portion by filling the inside and cooling the filled molten resin.

  In the above configuration, first, the connecting portion is molded using the first mold and the common mold. The first mold has an inner surface shape for forming the tip shape and the side surface shape of the connection portion. In particular, the tip shape of the connection portion is an inner surface so that a recess is formed in the center of the tip surface. A shape is provided. The common mold has an inner surface shape for forming the inner shape of the connecting portion.

  Next, when combined with a common mold, a second mold is prepared that enables a gasket molding cavity to be formed. This 2nd metal mold | die is equipped with the molten resin supply gate for supplying molten resin toward the said recessed part in the position facing the recessed part provided in the connection part. Then, the second mold and the common mold are closed with the connection portion held inside, and the molten resin is supplied into the cavity formed thereby from the molten resin supply gate. Since the molten resin supply gate is provided at a position facing the concave portion of the connecting portion, the supplied molten resin first flows into the concave portion and then spreads throughout the cavity. Thereafter, the molten resin filled in the cavity is cooled to form a gasket in a welded state between the connecting portion and its contact surface. Thus, in the above-described configuration, the degree of welding on the contact surface between the gasket and the connecting portion is controlled by controlling the flow state so that the molten resin flows into the concave portion of the connecting portion when supplying the molten resin. Is improved.

  In the manufacturing method, unlike the conventional plunger and gasket, the plunger is not directly connected to the gasket by a screw structure or the like. Since the gasket is connected to the plunger main body portion via the connection portion welded on the contact surface, the manufacturing method having the above configuration can omit an assembling operation for directly connecting the plunger to the gasket. In addition, the plunger can be manufactured without causing deformation of the gasket due to the displacement or distortion of the gasket that occurs during the assembly operation.

  In the above-described configuration, it is preferable that a plurality of groove portions are formed radially or spirally around the concave portion on the tip surface of the connection portion. For example, the molten resin supplied from a position facing the concave portion first flows into the concave portion, then flows through a groove portion provided radially from the concave portion, and spreads over the entire cavity. In this way, by guiding the flow direction of the molten resin, it is possible to further improve the non-uniform degree of welding on the contact surface between the gasket and the connecting portion.

  In the said structure, it is preferable to use what melt | dissolved the thermoplastic elastomer resin as said molten resin.

  In order to solve the above-described problems, a medical syringe of the present invention includes the syringe plunger described above and a syringe outer cylinder that slidably houses the syringe gasket. .

  According to the said structure, since the gasket is integrally provided by the welding part at the connection part of the plunger for syringes, the slack and detachment | leave between both can be prevented in use. Further, for example, an assembly operation for directly connecting the syringe plunger to the gasket plugged into the syringe outer cylinder is unnecessary. Therefore, the handleability is improved, and it is possible to prevent the occurrence of chemical leakage and bubble contamination due to the gasket displacement and distortion that occurred during the assembly operation.

  According to the present invention, the plunger is integrally provided with the gasket by welding at the connecting portion, and the concave portion is provided at the center of the distal end surface of the connecting portion. . Further, the concave portion functions as a molten resin receiving portion for receiving a molten resin for forming a gasket supplied at the time of forming the gasket, whereby the flow of the molten resin is in a turbulent state in the present invention. This can suppress the occurrence of non-uniform welding at the contact surface between the gasket and the connecting portion.

  As a result, for example, when the medical syringe is sterilized using an autoclave or the like performed before and after filling with a chemical solution, it is possible to suppress the occurrence of detachment on the welding surface between the gasket and the connection portion. In addition, since the smoothness of the gasket tip surface is not impaired by making the degree of welding uniform, the shape of the inner wall surface of the outer cylinder for a syringe that slidably accommodates the gasket is changed to the tip surface of the gasket. Can be adhered with high accuracy. As a result, in the medical syringe of the present invention, it is possible to discharge the medical solution filled in the syringe outer cylinder without leaving it. In addition, even when the medical syringe is installed at a position higher than the patient in a state where the medical syringe is filled with the medical solution, it is possible to prevent occurrence of detachment on the welding surface of the gasket and the connection portion. As a result, it is possible to prevent the so-called siphoning phenomenon in which the drug solution flows rapidly toward the patient. Further, it is possible to prevent the gasket from being detached from the connection portion even in the case of reverse blood performed to confirm that the patient is properly punctured.

  Furthermore, according to the present invention, the gasket accommodates at least a part of the connection part for connecting to the plunger main body part, and has a structure welded on the contact surface with the connection part. In this case, it is possible to prevent the slack and detachment from occurring between the gasket and the plunger main body. Furthermore, when using it, unlike the conventional plunger, the assembly work of directly connecting the plunger to the gasket becomes unnecessary, so that the handling is improved, and the position shift of the gasket that has occurred during the work is reduced. It is possible to prevent the occurrence of chemical leakage and bubble mixing due to shape deformation.

It is sectional drawing showing the medical prefilled syringe which concerns on Embodiment 1 of this invention. It is a side view showing the plunger for syringes and the outer cylinder for syringes in the said medical prefilled syringe. It is sectional drawing showing the outline of the said plunger for syringes. It is a cross-sectional schematic diagram showing the outline of the gasket in the said plunger for syringes, and the connection part accommodated in the said gasket, The same figure (b) is a top view showing the planar shape of a connection part, The figure (c). These are top views showing the planar shape of another connection part. The figure (a) is a side view showing the gasket in the said plunger for syringes, the figure (b) is sectional drawing showing the said gasket, and the figure (c) is a top view showing the said gasket. It is a cross-sectional schematic diagram showing the formation process of the connection part of the said plunger for syringes. It is a cross-sectional schematic diagram showing the formation process of the gasket of the said plunger for syringes. It is a cross-sectional schematic diagram showing the outline of the other connection part in the said plunger for syringes, Comprising: The same figure (a) represents the case where the convex part is provided in the position corresponding to the recessed part in the inner wall face of a connection part. FIG. 5B shows the case where the connecting portion does not include a flange portion. It is sectional drawing showing the plunger for syringes in the medical prefilled syringe which concerns on Embodiment 2 of this invention. The figure (a) is a side view showing the gasket and connection part in the said plunger for syringes, the figure (b) is sectional drawing showing the said gasket and connection part, The figure (c) is the said connection part. It is sectional drawing showing.

(Embodiment 1)
[Medical syringe]
A prefilled syringe will be described below as an example of a medical syringe (hereinafter referred to as “syringe”) of the present embodiment. FIG. 1 is a cross-sectional view showing the syringe. FIG. 2 is a side view showing a syringe plunger (hereinafter referred to as “plunger”) and a syringe outer cylinder (hereinafter referred to as “outer cylinder”) in the syringe.

  As shown in FIG.1 and FIG.2, the syringe 10 of this Embodiment is a plan provided with the outer cylinder 11 provided with the nozzle part 12 at the front-end | tip, the cap 3 which seals the nozzle part 12, and the gasket 23 in a connection part. A jar 21 and a chemical solution 6 filled in a chamber formed by the outer cylinder 11, the cap 3 and the gasket 23 are provided.

  The outer cylinder 11 includes a cylindrical portion 13 that is generally configured in a cylindrical shape, a nozzle portion 12 that is provided at the tip of the cylindrical portion 13, and a finger that is provided at the rear end of the cylindrical portion 13. And a grip 14. The length of the outer cylinder 11 is not particularly limited, and can be set as necessary.

  The outer cylinder 11 is preferably made of a material showing transparency or semi-transparency at least enough to visually recognize the inside, and more preferably made of a material having low oxygen permeability and water vapor permeability. . Such a material is not particularly limited, and examples thereof include polyvinyl chloride, polyethylene, polypropylene, polystyrene, polymethylpentene, polycarbonate, polyamide, acrylic resin, polyester such as polyethylene terephthalate, and cyclic olefin resin. Among these constituent materials, resins such as polypropylene, polyester, and poly- (4-methylpentene-1) are preferable from the viewpoints of ease of molding, shape stability, and production cost.

  The cylindrical part 13 is comprised with the bottomed cylindrical member. The diameter and length of the cylindrical part 13 are not specifically limited, It can set suitably. In the central portion of the bottom portion 15 in the tubular portion 13, a nozzle portion 12 having a reduced diameter with respect to the body portion of the tubular portion 13 is integrally formed. For example, a needle tube hub, connectors, and the like (not shown) are attached to the nozzle portion 12 and used.

  The nozzle portion 12 is located at the center (center opening) of the tubular portion 13 in the cross-sectional direction of the tubular portion 13 (that is, the direction perpendicular to the longitudinal direction of the tubular portion 13). However, the present embodiment is not limited to this, and may be provided at a position offset (lateral opening) from the center, for example. The diameter and height of the opening part of the nozzle part 12 are not specifically limited, It can set suitably. Further, an annular wall 17 is provided around the nozzle portion 12 so as to be separated by a certain distance. The height of the annular wall 17 is set to be lower than the height of the nozzle portion 12, and the nozzle portion 12 is provided so as to protrude from the opening tip of the annular wall 17. However, the present embodiment is not limited to this aspect, and may be an aspect in which the annular wall 17 is not provided. A cap 3 as a sealing member is detachably provided at the tip of the nozzle portion 12 in order to hermetically seal the lumen of the nozzle portion 12. In addition, this Embodiment is not limited to this aspect, For example, you may stick the sealing member which consists of a film etc.

  The finger grip 14 projects radially outward with respect to the cylindrical portion 13 and is integrally formed on the outer periphery of the proximal end of the outer cylinder 11. When the plunger 21 is moved relative to the outer cylinder 11, the finger grip 14 is put on the finger grip 14 for operation. When a known syringe pump is used, the finger grip 14 is fixed to the syringe pump, and the plunger 21 is moved relative to the outer cylinder 11 by pressing the pump. A scale 35 is formed on the outer peripheral surface of the cylindrical portion 13. Thereby, the liquid quantity of the chemical | medical solution 6 inside the syringe 10 can be grasped | ascertained.

  As shown in FIG. 3, the plunger 21 includes a plunger main body portion 20, a connection portion 24 provided at the front end of the plunger main body portion 20, and a gasket that accommodates a part of the connection portion 24 from the rear end side. 23 at least.

  The plunger body 20 includes a plunger shaft portion 22 having a cross-shaped cross section, a male screw portion 43 provided in front of the plunger shaft portion 22, and a gasket pressing portion 25 provided at the rear end of the male screw portion 43. And a plunger pressing disk portion 26 provided at the rear end portion of the plunger shaft portion 22, which is formed of the same material and has an integral structure. The plunger main body portion 20 and the connection portion 24 have a structure that can be connected by screwing between the female screw portion 24 c in the connection portion 24 and the male screw portion 43 provided on the gasket pressing portion 25. However, the present invention is not limited to this aspect, and the plunger main body 20 and the connecting portion 24 may be integrally formed of the same material.

  Plunger 21 is made of high-density polyethylene, polypropylene, polystyrene, butadiene-styrene copolymer, acrylonitrile-butadiene-styrene copolymer, polymethylpentene, polycarbonate, acrylic resin, polyethylene terephthalate, cyclic polyolefin, etc., except for gasket 23. It is made of hard or semi-hard resin. However, this embodiment mode is not limited to this material, and other constituent materials can be used as appropriate. Moreover, the plunger main body 20 and the connecting portion 24 may be made of different materials.

  As shown in FIGS. 4A and 4B, the connecting portion 24 has a top portion 24a having a substantially conical shape and a main body portion 24b having a cylindrical shape. FIG. 4A is a schematic cross-sectional view illustrating the outline of the connecting portion 24 accommodated in the gasket 23, and FIG. 4B is a plan view illustrating the planar shape of the connecting portion 24. By making the top portion 24a substantially conical, the fluidity of the molten resin for forming the gasket supplied when the gasket 23 is formed can be improved. In addition, the shape of the connection part 24 is not limited to the said aspect, For example, the top part 24a may be a substantially polygonal cone shape, and the main-body part 24b may be a polygonal column shape.

  As shown in FIG. 4B, one concave portion 27 is provided at the center of the tip surface of the connecting portion 24 (the top portion 24a). The concave portion 27 functions as a molten resin receiving portion for receiving a molten resin for forming a gasket supplied when the gasket 23 is formed. For example, when molten resin is supplied into the cavity for molding the gasket from a position facing the recess, the molten resin first flows into the recess 27 with respect to the connecting portion 24 and then fills the entire cavity. . By controlling the flow of the molten resin in this way, it is possible to improve the degree of welding of the contact surface between the inner wall surface of the gasket 23 and the connection portion 24 from becoming uneven.

  The opening shape of the concave portion 27 in plan view is a substantially circular shape (see FIG. 4B). Thereby, after the recessed part 27 receives the molten resin for gasket formation, the molten resin can be prevented from being unevenly distributed in a specific direction and flowing. However, the opening shape of the concave portion 27 is not particularly limited as long as the concave portion 27 can be molded, and may be, for example, a rectangular shape or a polygonal shape. Moreover, the diameter of the opening shape of the recessed part 27 is not specifically limited, It can set suitably as needed.

  The depth shape of the concave portion 27 (the cross-sectional shape of the concave portion 27 in a sectional view) is tapered. Thereby, the mold release property from the metal mold | die of the shape | molded connection part 24 can be improved. However, the depth shape of the recess 27 is not particularly limited as long as the recess 27 can be formed. For example, the wall surface of the recess 27 may be a vertical wall surface. Also, the bottom surface of the recess 27 may be a round bottom. The lower limit value of the maximum depth of the recess 27 is preferably 0.1 mm or more, more preferably 0.2 mm or more, and particularly preferably 0.5 mm or more. Further, the upper limit value of the maximum depth of the recess 27 is preferably 2 mm or less, more preferably 1.5 mm or less, and particularly preferably 1 mm or less. By setting the lower limit of the maximum depth of the recess 27 to 0.1 mm or more, the function as the molten resin receiving portion can be improved. On the other hand, by setting the upper limit value of the maximum depth of the concave portion 27 to 2 mm or less, it is possible to prevent the function of the concave portion 27 as the molten resin receiving portion from being impaired. That is, when the depth of the concave portion 27 exceeds the upper limit value, the molten resin that first flows into the concave portion 27 is retained, so that hardening by cooling starts and the flow of the molten resin that is filled later is in a turbulent state. It may become. Therefore, by setting the depth of the concave portion 27 to 2 mm or less, the molten resin that first flows into the concave portion 27 can be prevented from staying, and the function of the concave portion 27 as the molten resin receiving portion can be maintained.

  Moreover, 0.2 mm or more is preferable and, as for the lower limit of the maximum thickness of the connection part 24 in the part in which the recessed part 27 is provided, 1 mm or more is more preferable. On the other hand, the upper limit value of the maximum thickness of the connecting portion 24 is preferably 3 mm or less, and more preferably 2 mm or less. By setting the lower limit value of the maximum thickness of the connecting portion 24 to 0.2 mm or more, the space volume of the cavity is secured and the supplied molten resin can flow. On the other hand, by setting the upper limit value of the maximum thickness of the connecting portion 24 to 3 mm or less, it is possible to prevent the cooling time of the molten resin from being prolonged. In addition, it is possible to prevent appearance defects and shape defects such as sink marks (surface dent deformation caused by molding shrinkage).

  The rear end side of the main body portion 24b of the connection portion 24 is open, and a female screw portion 24c is provided therein. Thereby, screwing with the external thread part 43 provided on the gasket press part 25 is attained. The plunger 21 of the present embodiment is not directly connected to the gasket 23 by a screw structure or the like. The plunger main body 20 is joined by screwing to a connecting portion 24 that is welded on the contact surface inside the gasket 23. This prevents the gasket from being displaced, distorted, or deformed when the plunger is directly connected to the gasket with a screw structure or the like. Can be prevented.

  Further, a flange portion 28 is provided on the connection portion 24 on the connection side with the plunger main body portion 20, that is, on the rear end side of the main body portion 24b. The flange portion 28 has an annular shape projecting radially outward with respect to the main body portion 24b. The diameter of the flange portion 28 is substantially the same as the diameter of the outer peripheral surface of the gasket 23, so that the flange portion 28 is flush with the outer peripheral surface of the gasket 23. Since the connecting portion 24 includes the flange portion 28, when the plunger 21 is accommodated in the outer cylinder 11 of the syringe 10 and combined, the flange portion 28 is brought into contact with the inner peripheral surface of the syringe 10. It becomes possible to make it. As a result, it is possible to prevent the plunger 21 from sliding while swinging, and the sliding performance of the plunger 21 relative to the outer cylinder 11 of the syringe 10 can be improved.

  Further, as shown in FIG. 4C, the front end surface of the connecting portion 24 (the top portion 24 a) may be connected to the concave portion 27, and a plurality of groove portions 29 may be provided radially around the concave portion 27. Good. Thereby, the molten resin for forming a gasket that has flowed into the recess 27 is guided by the groove 29 and can flow radially from the recess 27. As a result, it is possible to suppress the occurrence of turbulent flow in the flow of the molten resin. The number of grooves 29 is not particularly limited, and can be set as necessary. Further, the depth shape of the groove 29 (the cross-sectional shape in a direction perpendicular to the direction in which the groove 29 extends) is not particularly limited as long as the groove 29 can be formed. Specific examples of the depth shape of the groove portion 29 include a V shape. Further, the depth of the groove 29 is preferably the same as the depth of the recess 27. Thereby, it can further reduce that the flow of molten resin will be in a turbulent state.

  All the groove parts 29 have the same length, and extend from the concave part 27 to the peripheral part in the top part 24a. Moreover, the length of the groove part 29 is not specifically limited, It can set suitably according to the magnitude | size etc. of the top part 24a. For example, each groove portion 29 may extend until it reaches the circumferential portion at the top portion 24a. Further, the lengths of the grooves 29 in the extending direction may be different from each other. In this case, for example, a long groove portion and a short groove portion in the extending direction may be alternately arranged. Thereby, the molten resin can be made to flow radially with a uniform flow amount around the recess 27.

  Each groove 29 extends at the same depth. Moreover, the lower limit of the depth of the groove part 29 is preferably 0.1 mm or more, more preferably 0.2 mm or more, and particularly preferably 0.5 mm or more. Moreover, the upper limit of the depth of the groove part 29 is preferably 2 mm or less, more preferably 1.5 mm or less, and particularly preferably 1 mm or less. By setting the lower limit value of the depth of the groove 29 to 0.1 mm or more, the function as a guide for the flowing molten resin can be maintained. On the other hand, by setting the upper limit of the depth of the groove 29 to 2 mm or less, it is possible to prevent the function of guiding the flow of the molten resin from being impaired. Furthermore, the depth of each groove part 29 may be an aspect that gradually decreases as the distance from the concave part 27 increases in the extending direction. Moreover, the depth of each groove part 29 may mutually differ. In this case, for example, a deep groove portion and a shallow groove portion in the extending direction may be alternately arranged. Thereby, the molten resin can be made to flow radially with a uniform flow amount around the recess 27.

  The width of the groove 29 (the width in the direction perpendicular to the extending direction) is not particularly limited as long as it is the same as or smaller than the diameter of the recess 27. However, the groove 29 preferably has a width that allows the molten resin to flow from the center of the top 24a to the peripheral edge. Moreover, although the width | variety of the groove part 29 is the same from the recessed part 27 to the peripheral part of a top part, this invention is not limited to this. For example, an aspect in which the width of the groove 29 gradually increases as the distance from the concave portion 27 in the extending direction or an aspect in which the width becomes narrower may be employed.

  Furthermore, although the groove part 29 of this Embodiment is radially extended from the center recessed part 27 to the peripheral part in the top part 24a, this invention is not limited to this aspect. For example, the aspect extended spirally centering on the recessed part 27 may be sufficient. In this case, the flow path of the molten resin to be flowed can be extended, and the number of places where the molten resin stays can be reduced.

  The constituent material of the connection part 24 is not particularly limited. For example, high-density polyethylene, polypropylene, polystyrene, butadiene-styrene copolymer, acrylonitrile-butadiene-styrene copolymer, polymethylpentene, polycarbonate, acrylic resin, polyethylene terephthalate, Examples thereof include hard or semi-rigid resins such as cyclic polyolefin. In addition, as the constituent material of the connecting portion 24, a polyvinyl chloride-based thermoplastic elastomer resin, a polyolefin-based thermoplastic elastomer resin, a styrene-based thermoplastic elastomer resin, a polyester-based thermoplastic elastomer resin, a polyamide-based thermoplastic elastomer resin, a polyurethane-based material Examples thereof include thermoplastic elastomer resins and thermoplastic elastomer resins such as a mixture thereof. In selecting the constituent material of the connecting portion 24 from these materials, it is preferable to select a material that can make the hardness of the connecting portion 24 larger than the hardness of the gasket 23. Further, the constituent material of the connecting portion 24 may be the same as or different from the constituent material of the plunger 21. When considering the hardness of the plunger 21, it is preferable to select a material having a hardness equal to or higher than that of the plunger 21 in selecting the constituent material of the connection portion 24.

  As shown in FIGS. 1 and 2, the gasket 23 is slidably accommodated in the cylindrical portion 13 of the outer cylinder 11. As shown in FIGS. 5A to 5C, the gasket 23 includes a gasket main body portion 31 that extends with substantially the same outer diameter, a closing portion 33 at the tip of the gasket main body portion 31, and a gasket main body portion 31. And an opening 34 at the rear end. The gasket 23 is solid. Fig.5 (a) is a side view showing the gasket in the said plunger for syringes, FIG.5 (b) is sectional drawing showing the said gasket, FIG.5 (c) is a top view showing the said gasket. The opening portion 34 is provided in the gasket 23 in order to accommodate at least a part of the connection portion 24.

  The closing portion 33 has a shape conforming to the shape of the inner wall surface of the bottom portion 15 so as not to form a gap as much as possible when contacting the inner wall surface of the bottom portion 15 of the outer cylinder 11. Further, the connecting portion 24 is accommodated in the opening 34 of the gasket, and the inner wall surface of the opening 34 and the connecting portion 24 are welded to each other on the contact surface without any gap, and have an integral structure. That is, the gasket 23 has an integral structure as a part of the plunger 21. A convex portion 36 is provided on the inner wall surface of the gasket 23 at a position corresponding to the concave portion 27 of the connecting portion 24. As described later, the term “welding” refers to a result of melting of the surface of the connecting portion 24 in contact with the heat of the molten resin injected when the gasket 23 is molded by injection molding or the like. This means that the gasket 23 and the connecting portion 24 are in a combined state at the contact surface after the molding.

  An annular rib 32 is provided between the gasket main body 31 and the closing portion 33 and at the rear end of the gasket main body 31. The annular rib 32 is in liquid-tight contact with the inner wall surface of the cylindrical portion 13 of the outer cylinder 11. The number of the annular ribs 32 is not particularly limited as long as the liquid tightness and slidability of the gasket 23 can be maintained.

  The gasket 23 is not particularly limited as long as it is made of an elastic material, and a conventionally known gasket can be used. The elastic material means a material that can be deformed to such an extent that the annular rib 32 of the gasket 23 comes into liquid-tight contact with the inner wall surface of the cylindrical portion 13 when the plunger 21 is accommodated in the outer cylinder 11. More specifically, for example, thermoplastic elastomer resins, polyolefin resins, fluorine resins, and polyester resins can be used. Examples of the thermoplastic elastomer resin include a polyvinyl chloride thermoplastic elastomer resin, a polyolefin thermoplastic elastomer resin, a styrene thermoplastic elastomer resin, a polyester thermoplastic elastomer resin, a polyamide thermoplastic elastomer resin, and a polyurethane thermoplastic. Elastomeric resins and mixtures thereof are preferred.

  Of these constituent materials, styrene-based thermoplastic elastomer resins and polyester-based thermoplastic elastomer resins are preferred in the present embodiment. Regarding the polyester-based thermoplastic elastomer resin, although it depends on the type of the constituent material of the connecting portion 24, it can be made to have excellent weldability with the connecting portion 24 of the plunger 21 and prevent the plunger 21 from being detached. Can do. In addition, since the polyester-based thermoplastic elastomer resin is excellent in heat resistance and wear resistance, thermal deformation can be prevented even during sterilization of a chemical solution. As a result, it is possible to prevent liquid leakage due to the thermal deformation and prevent bubbles from being mixed into the chemical liquid. A commercially available product can be used as the polyester-based thermoplastic elastomer resin. Examples of such commercially available products include Primalloy (registered trademark, manufactured by Mitsubishi Chemical Corporation), Hytrel (registered trademark, manufactured by Toray DuPont Co., Ltd.), and the like.

  A lubricant may be applied to the surface of the gasket 23. Thereby, the slidability with respect to the inner wall surface of the cylindrical portion 13 of the outer cylinder 11 can be further improved. The lubricant is not particularly limited, and for example, silicone oil or the like can be used.

  The gasket pressing portion 25 has a disk shape, and the gasket 23 can be pressed via the connecting portion 24 when the plunger 21 is moved and operated relative to the outer cylinder 11. Moreover, since the peripheral part of the gasket pressing part 25 is in contact with the gasket 23, the gasket 23 can be directly pressed at the peripheral part. The thickness of the gasket pressing part 25 is not specifically limited, It can set suitably as needed. Moreover, the diameter of the gasket pressing part 25 should just be a grade which the plunger 21 can slide in the outer cylinder 11, and is set so that it may become smaller than the internal diameter of the cylindrical part 13 of the outer cylinder 11. FIG. .

  The plunger pressing disk portion 26 has a disk shape, and the thickness thereof is not particularly limited, and may be set as necessary. Further, the diameter of the disk portion 26 is not particularly limited, and may be set as necessary. Furthermore, instead of the disk portion 26, a polygonal plate shape may be used.

  It does not specifically limit as the chemical | medical solution 6, A conventionally well-known prefilled syringe formulation etc. can be used suitably.

[Manufacturing method of plunger for syringe]
Next, the manufacturing method of the plunger 21 of this Embodiment is demonstrated below based on FIG.6 and FIG.7. FIG. 6 is a schematic cross-sectional view illustrating a molding process of the connecting portion 24 of the plunger 21. FIG. 7 is a schematic cross-sectional view illustrating a molding process of the gasket 23 of the plunger 21.

  The manufacturing method of the plunger 21 of the present embodiment includes a step of forming the connection portion 24 using the first die and the common die, and a second die so as to be welded to the connection portion 24 on the contact surface. And a step of forming the gasket 23 using a common mold. In the present embodiment, the connecting portion 24 and the gasket 23 are molded using a two-color molding method.

  First, as shown in FIG. 6A, the forming step of the connecting portion 24 includes a first mold 51 having an inner surface shape for forming a tip shape and a side shape of the connecting portion 24, and an inner side of the connecting portion 24. A common mold 52 having an inner surface shape for forming the shape is prepared. The first mold 51 is a core (convex mold), and the common mold 52 is a cavity (concave mold). The first mold 51 and the common mold 52 have a structure in which a cavity capable of forming the connection portion 24 is formed when the mold is closed. The first mold 51 is provided with a concave molding convex portion 53 so that the concave portion 27 is formed at the center of the tip surface of the connecting portion 24 to be molded. The first mold 51 includes a first molten resin supply gate 54 for supplying a molten resin obtained by melting a resin that is a constituent material of the connection portion 24. In the present embodiment, the first molten resin supply gate 54 is disposed at the center of the first mold 51, but the present invention is not limited to this. For example, the installation position of the first molten resin supply gate 54 can be appropriately set such that the molten resin flows from a thick portion to a thin portion of the connecting portion 24 to be molded.

  6B, the first mold 51 and the common mold 52 are closed as shown in FIG. 6B, and then the constituent material of the connection part 24 is formed as shown in FIG. A molten resin 55 obtained by melting the resin to be used is injected into the cavity. The injection pressure of the molten resin is not particularly limited, and can be set as necessary. The injected molten resin is cooled in a closed state. The cooling time is not particularly limited, and can be set as necessary. After the mold opening, as shown in FIG. 6 (d), a recess 27 is formed at the center of the tip surface, and a connection part 24 provided with a female screw part 24c is formed inside.

  Next, the gasket 23 is molded (see FIGS. 7A to 7D). In forming the gasket 23, the second mold 56 and the common mold 52 are used. The gasket 23 is molded in a state where the connection portion 24 is placed inside the second mold 56 and the common mold 52 which are closed. The second mold 56 is a core (convex type). The second mold 56 and the common mold 52 have a structure in which a cavity capable of forming the gasket 23 is formed when the mold is closed. Further, the second mold 56 is provided with a second molten resin supply gate (molten resin supply gate) 57 for supplying a molten resin obtained by melting a resin that is a constituent material of the gasket 23. The second molten resin supply gate 57 is provided so as to face the recessed portion 27 of the connection portion 24 placed inside the second mold 56 and the common mold 52 which are closed.

  As shown in FIG. 7B, the molding of the gasket 23 is performed by closing the second mold 56 and the common mold 52, and then, as shown in FIG. A molten resin 58 obtained by melting the resin is injected into the cavity. Here, since the second molten resin supply gate 57 is provided at a position facing the concave portion 27 of the connecting portion 24, the supplied molten resin 58 first flows into the concave portion 27 and then spreads throughout the cavity. Thereby, it can improve that the grade of the welding in the contact surface of the gasket 23 and the connection part 24 becomes non-uniform | heterogenous.

  The injection pressure of the molten resin 58 is not particularly limited, and can be set as necessary. Further, the filling speed of molten resin 58 (the speed from the injection of molten resin 58 into the cavity to the end of filling) is not particularly limited, and can be appropriately set according to the injection pressure or the like. After injecting the molten resin 58, a pressure holding step of applying pressure to the molten resin 58 and compressing (pressure control) may be performed in order to compensate for the cooling shrinkage of the molten resin 58. Thereafter, the injected molten resin 58 is cooled in a closed state. The cooling time is not particularly limited, and can be set as necessary. After the mold opening, as shown in FIG. 7D, the front end is closed, and the gasket 23 accommodating the connection portion 24 is formed from the opening 34 at the rear end. Further, the inner wall surface of the gasket 23 is welded on the contact surface including the concave portion 27 of the connecting portion 24.

  In addition, it does not specifically limit as a method to take out the molded gasket 23 and the connection part 24 from the common metal mold | die 52, The method by various rotation extraction can be employ | adopted. Specifically, for example, a motor rack method, a rack and pinion method (by a mold opening / closing movement), a forced removal method, an in-division slide method, and the like can be given. The motor rack system is a system in which a motor is used as a power source for transmitting rotation to the screw core for forming the female screw portion 24 c on the inner wall surface of the connection portion 24. The rack and pinion system is a system in which the opening and closing motion of the molding machine is transmitted by a rack and gears, and the screw core is rotated. The forced removal method is a method in which the molded gasket 23 and the connection portion 24 are forcibly removed from the common mold 52. The in-division slide method is a method in which die cutting is easily performed by dividing the screw core into a plurality of parts after molding. Among these methods, from the viewpoint that the screw thread of the female screw portion 24c is increased and the screwed structure with the male screw portion 43 provided in the plunger main body portion 20 can be strengthened, the motor rack method, the rack -An and pinion system (by mold opening / closing movement) and a slide-in-segment slide system are preferred. Further, among these methods, the motor rack method is particularly preferable from the viewpoint of suppressing the equipment cost.

  On the other hand, the plunger main body 20 can also be produced separately by using a known molding method. Specifically, an injection molding method etc. are mentioned, for example. Thereafter, the plunger main body part 20 and the connection part 24 are connected by screwing the male screw part 43 of the plunger main body part 20 and the female screw part 24c of the connection part 24, and this embodiment relates. Plunger 21 can be made.

[Other matters]
With respect to the structure of the gasket and the connecting portion accommodated in the gasket, in the present embodiment, for example, a structure as shown in FIG. 8A or FIG. 8B may be employed. FIG. 8 is a schematic cross-sectional view showing an outline of another connecting portion. FIG. 8A shows a case where a convex portion is provided at a position corresponding to the concave portion on the inner wall surface of the connecting portion. FIG. 5B shows a case where the connection portion does not include a flange portion.

  As shown in FIG. 8A, the connecting portion 24 'has a flat shape with no apex at the tip as a whole, and includes a cylindrical main body portion 24b. Since the connecting portion 24 ′ does not have a substantially conical top portion, the gasket 23 is thick. A concave portion 27 is provided at the center of the front end surface of the connecting portion 24 ′. However, in the structure shown in FIG. 8, a convex portion 37 is also provided at a position corresponding to the concave portion 27 on the inner wall surface of the connecting portion 24 ′. It has been. The convex portion 37 corresponds to the concave portion 27. Accordingly, the planar shape of the convex portion 37 is the same as the opening shape of the concave portion 27, and a substantially circular shape, rectangular shape, polygonal shape, or the like can be adopted. Further, the height of the convex portion 37 is substantially the same as the depth of the concave portion 27, and the size of the convex portion in plan view is the same as the opening shape of the concave portion 27. By providing the convex portion 37 corresponding to the concave portion 27 on the inner wall surface of the connecting portion 24 ′, the thickness of the central portion of the tip surface where the concave portion 27 is provided can be made the same as other portions. As a result, it is possible to suppress a decrease in mechanical strength at the center portion of the tip surface of the connection portion 24 ′.

  Further, as shown in FIG. 8B, the connection portion 24 ″ has a structure that does not include the flange portion 28 as compared with the connection portion 24, and is entirely accommodated in the gasket 23.

(Embodiment 2)
A second embodiment of the present invention will be described below with reference to FIGS. Note that members having the same functions as those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted. FIG. 9 is a cross-sectional view illustrating a plunger for a syringe in the medical prefilled syringe according to the second embodiment. FIG. 10A is a side view showing a gasket and a connecting portion in the syringe plunger, FIG. 10B is a cross-sectional view showing the gasket and the connecting portion, and FIG. 10C is the connecting portion. It is sectional drawing showing.

  The second embodiment is common to the first embodiment in that the gasket 23 is integrally provided by welding with the connecting portion 61 as shown in FIGS. 9 and 10. Further, the plunger 21 and the connecting portion 61 can be connected and separated by screwing between the female screw portion 24 c provided in the connecting portion 61 and the male screw portion 43 provided on the gasket pressing portion 25. This is also common to the first embodiment. However, the second embodiment is different from the first embodiment in the structure of the connecting portion 61.

  That is, the connecting portion 61 of the present embodiment has a substantially cylindrical structure in which the top portion 24 a is substantially conical and the main body portion 62 has an annular stepped portion 63. The step portion 63 is provided in an annular shape in the cross-sectional direction of the main body portion 62 (that is, the direction perpendicular to the longitudinal direction of the main body portion 62). In the main body 62, the upper part 62 a above the step part 63 is accommodated in the gasket 23. Further, in the main body 62, the lower portion 62 b below the stepped portion 63 has a diameter that is substantially the same as the diameter of the outermost surface of the gasket main body 31 of the gasket 23, and is flush with the side peripheral surface of the gasket 23. It has become.

  On the inner wall surface of the lower part 62 b in the main body 62, a female screw part 24 c that enables screwing with the male screw part 43 provided in front of the plunger shaft part 22 is provided. Therefore, when the plunger main body 20 and the connecting portion 61 are connected by screwing the male screw portion 43 and the female screw portion 24c, the space 64 is formed inside the connecting portion 61 and becomes hollow.

  In the present embodiment, the space 64 is formed inside the connecting portion 61, so that the thickness of the upper portion 62 a of the main body portion 62 accommodated in the gasket 23 can be reduced. Thereby, since the compression deformation of the upper part 62a is attained, the workability | operativity at the time of accommodating and combining the plunger 21 in the outer cylinder 11 of the syringe 10 can be aimed at. Here, the thickness of the upper part 62a is preferably in the range of 0.2 mm to 1.5 mm, and more preferably in the range of 0.3 mm to 1.5 mm. By setting the thickness of the upper part 62a to 0.2 mm or more, it is possible to prevent the molding failure of the upper part 62a and to ensure the shape stability. On the other hand, when the thickness of the upper part 62a is 1.5 mm or less, although it depends on the material of the connection part 61, it is possible to prevent the compression deformation from becoming difficult.

  The connecting portion (not shown) may have a flat shape with no top at the tip as a whole, and may have a structure consisting only of the main body portion 62. In this case, the gasket 23 is thick because the connecting portion does not have a substantially conical top portion. In addition, a convex portion is provided at a position corresponding to the concave portion 27 on the inner wall surface of the connection portion. Thereby, the thickness of the center part of the front-end | tip surface in which the recessed part 27 was provided can be made the same as that of another part. As a result, it is possible to suppress a decrease in mechanical strength at the center portion of the tip surface of the connection portion.

(Other matters)
In the first and second embodiments, the case where the plunger main body portion and the connection portion are connected by a screwing structure has been described as an example, but the present invention is not limited to this aspect. For example, the plunger main body portion and the connection portion may be connected by a fitting structure. In this case, for example, a mode in which a convex portion is provided in the plunger main body portion and a concave portion that can be fitted to the convex portion is provided in the connection portion.

  In the first and second embodiments, the case of a prefilled syringe has been described as an example, but the present invention is not limited to these embodiments. For example, it can also be used for blood sampling syringes, balloon syringes, experimental general syringes, and the like.

10 (medical) syringe 11 (for syringe) outer cylinder 12 nozzle portion 13 tubular portion 14 finger grip 15 bottom portion 17 annular wall 20 plunger main body portion 21 (for syringe) plunger 22 plunger shaft portion 23 gasket 24 connecting portion 24 Main body portion 24a Top portion 24b Main body portion 24c Female screw portion 25 Gasket pressing portion 26 Disc portion 27 Recess 28 Flange portion 29 Groove portion 31 Gasket main portion 32 Annular rib 33 Closure portion 34 Opening portion 36, 37 Convex portion 43 Male screw portion 51 Gold Mold 52 Common mold 53 Convex molding convex part 54 First molten resin supply gate 55 Molten resin 56 Mold 57 Second molten resin supply gate 58 Molten resin 61 Connection part 62 Body part 62a Upper part 62b Lower part 63 Step part 64 Space

Claims (10)

A plunger body,
A connecting portion provided at a tip of the plunger main body,
A plunger for a syringe provided with a gasket whose front end is closed and whose rear end is opened, wherein at least a part of the connection portion is accommodated from the rear end side.
A concave portion is provided at the center of the tip surface of the connecting portion,
The concave portion is a molten resin receiving portion for receiving a molten resin for forming a gasket supplied at the time of forming the gasket,
The plunger for a syringe, wherein the gasket is welded to a contact surface including at least the connection portion and the recess.   The plunger for a syringe according to claim 1, wherein a plurality of groove portions are provided radially or spirally around the concave portion on a front end surface of the connection portion. On the connection side of the connection portion with the plunger main body portion, a flange portion protruding radially outward is provided,
The syringe plunger according to claim 1 or 2, wherein a diameter of the flange portion is substantially the same as a diameter of an outer peripheral surface of the gasket. The connection portion includes a female screw portion therein, and the plunger main body portion includes a male screw portion screwed into the female screw portion,
The syringe plunger according to any one of claims 1 to 3, wherein the connection portion and the plunger main body portion are joined together by a screwing structure. The connection portion has a main body portion provided with an annular step portion, and a top portion provided at the tip of the main body portion,
The female screw portion is provided on the rear end side from the formation position of the step portion in the main body portion,
The inside of the connection part is hollow on the top side of the stepped part by joining with the plunger main body part by a screwing structure with the connection part. The plunger for syringe as described.   The plunger for a syringe according to any one of claims 1 to 4, wherein the gasket is made of a thermoplastic elastomer resin. A plunger body,
A connecting portion provided at a tip of the plunger main body,
In a method for manufacturing a plunger for a syringe, comprising a gasket having a closed front end and a rear end opened, wherein at least a part of the connection portion is accommodated from the rear end side.
Using a first mold having an inner surface shape for forming the tip shape and side surface shape of the connection portion, and a common mold having an inner surface shape for forming the inner shape of the connection portion, the tip surface Forming the connecting portion having a recess in the center of the
When combined with the common mold, a molten resin supply gate is provided that can form a cavity for molding the gasket and supplies the molten resin toward the concave portion at a position facing the concave portion in the connecting portion. The second mold is provided, the mold is closed with the common mold while the connection portion is held inside, and the molten resin is supplied from the molten resin supply gate to be filled in the cavity. A method for manufacturing a plunger for a syringe, comprising: cooling the molten resin to form the gasket welded on the contact surface including at least the concave portion.   The method for manufacturing a plunger for a syringe according to claim 7, wherein a plurality of grooves are formed radially or spirally around the concave portion on a front end surface of the connection portion.   The manufacturing method of the plunger for syringes of Claim 7 or 8 which uses what melt | dissolved the thermoplastic elastomer resin as said molten resin.   A medical syringe comprising the syringe plunger according to any one of claims 1 to 6 and a syringe outer cylinder that slidably accommodates the syringe gasket.

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