CN109641108B

CN109641108B - Plunger for syringe, method for producing same, and medical syringe

Info

Publication number: CN109641108B
Application number: CN201780050224.5A
Authority: CN
Inventors: 铃木启介; 大浦知之
Original assignee: Inside And Outside Chemical Co ltd
Current assignee: Inside And Outside Chemical Co ltd
Priority date: 2016-09-05
Filing date: 2017-08-25
Publication date: 2021-07-23
Anticipated expiration: 2037-08-25
Also published as: WO2018043356A1; CN109641108A; JP6889921B2; JP2018038813A

Abstract

The invention provides a plunger for a syringe, a manufacturing method thereof and a medical syringe, wherein the welding degree of the contact surface between a gasket and a plunger body is uniform, and the separation of the gasket and the plunger body and the displacement of the gasket and the shape deformation caused by deformation when the plunger body is installed on the gasket can be prevented. A plunger (21) for a syringe is provided with: a plunger body (20); a connecting part (24) provided at the front end of the plunger body part (20); the gasket (23) is closed at the front end and opened at the rear end, and at least a part of the connecting part (24) is accommodated from the rear end side, a concave part (27) is provided at the center part of the front end surface of the connecting part (24), the concave part (27) is a molten resin receiving part for receiving molten resin for gasket molding supplied at the time of gasket molding (23), and the inner wall surface of the gasket (23) and the connecting part (24) are welded together at a contact surface including at least the concave part (27).

Description

Plunger for syringe, method for producing same, and medical syringe

Technical Field

The present invention relates to a plunger for a syringe, a method for manufacturing the same, and a medical syringe, and more particularly, to a plunger for a syringe, a method for manufacturing the same, and a medical syringe, which can prevent the occurrence of positional displacement and shape deformation of a gasket.

Background

In recent years, a large number of prefilled syringes filled with a liquid medicine in advance have been used. A method called a vacuum cap is used for inserting a gasket in a prefilled syringe, in which a medical solution is filled in an outer tube in which a distal end opening is sealed, the gasket is disposed in the opening of the outer tube under a reduced pressure atmosphere (vacuum atmosphere), and then the gasket is inserted into the outer tube under a normal pressure. In addition, in a prefilled syringe, a plunger is attached to a gasket after a cap sealing operation of the gasket, and in such a system, in order to facilitate attachment of the plunger to the gasket, prevent leakage at the time of attachment, and suppress an increase in internal pressure, usually, an external thread portion is provided in the plunger, and an internal thread portion is provided in the gasket, and both are connected by screwing (for example, see patent document 1 below).

However, in the structure in which the plunger and the gasket are connected by screwing, the plunger may be loosened during assembly or use, and the plunger may be detached. Further, when the plunger and the gasket are connected, the plunger needs to be screwed into the outer cylinder for syringe while rotating the plunger, and if the plunger is pressed into the outer cylinder without rotating the plunger, the plunger is difficult to screw into the gasket. As a result, the gasket that is previously closed may be pressed by the plunger, and the shape of the gasket may be deformed, such as displacement or deformation. This causes a problem of leakage of the medical solution filled in the outer cylinder for syringe and mixing of air bubbles.

Patent document 2 discloses a plunger for a medical syringe, in which a member of a plunger body corresponding to a female screw portion is provided inside a piston body corresponding to a gasket, and the member is screwed into a second member of the plunger body corresponding to a male screw portion, thereby connecting the members. According to this patent document, the piston body and the plunger body are welded to each other at the contact surface.

However, in patent document 2, no consideration is given to making the degree of fusion at the contact surface between the piston main body and the member of the plunger main body uniform. Therefore, for example, when sterilization treatment using an autoclave or the like is performed before and after filling of the chemical solution, there is a problem that the parts of the piston main body and the plunger main body are separated at the contact surface where the piston main body and the plunger main body are welded together. Further, if the degree of welding is not uniform, the smoothness of the front end surface of the piston main body is impaired, and unevenness may occur. If the front end surface of the piston body is uneven, it is difficult to discharge the drug solution filled in the syringe without leaving any residue.

In addition, 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 liquid, a so-called siphon phenomenon occurs in which the medical liquid rapidly flows to the patient due to a pressure difference caused by the difference in level. Therefore, although the plunger body is generally fixed to a syringe pump device or the like to prevent the occurrence of the siphon phenomenon, if the degree of fusion bonding at the contact surface between the piston body and the member of the plunger body is not uniform as described above, the piston body is separated from the member of the plunger body even if the plunger body is fixed, and as a result, the siphon phenomenon occurs, and the drug solution rapidly flows to the patient. Further, when blood is returned to confirm that the patient has properly punctured, there is also a problem that the piston body is detached from the plunger body.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2003-159330

Patent document 2: japanese Kokai publication No. 2006-502896

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made in view of the above problems, and an object of the present invention is to provide a syringe plunger, a method of manufacturing the same, and a medical syringe, in which the degree of fusion bonding at the contact surface between a gasket and a plunger body is uniform, and separation of the gasket and the plunger body, and occurrence of positional displacement of the gasket and shape deformation due to deformation when the plunger body is attached to the gasket can be prevented.

Means for solving the problems

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

In order to solve the above problem, a syringe plunger according to the present invention includes: a plunger body portion; a connecting portion provided at a front end of the plunger body portion; and a gasket having a closed front end and an open rear end, and accommodating at least a part of the connecting portion from the rear end side, wherein a recess is provided in a central portion of a front end surface of the connecting portion, the recess being a molten resin receiving portion for receiving a molten resin for gasket molding supplied at the time of gasket molding, and the gasket and the connecting portion are welded together at a contact surface including at least the recess.

According to this structure, the plunger main body portion and the gasket are connected via the connecting portion. That is, the plunger for syringe (hereinafter, also referred to as "plunger") is configured such that the coupling portion is provided at the front end of the plunger body portion, and the gasket accommodates at least a part of the coupling portion from the rear end side of the opening. The gasket and the connecting portion are welded together at the contact surface, thereby forming an integral structure. A recess is provided in the center of the front end surface of the connecting portion, and the recess is also welded to the inner wall surface of the gasket. The recessed portion functions as a molten resin receiving portion for receiving molten resin for gasket molding supplied at the time of gasket molding. Therefore, for example, when molten resin is supplied into the cavity for gasket molding from a position facing the recessed portion, the molten resin flows into the recessed portion 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 situation in which the degree of fusion at the contact surface between the gasket and the connecting portion becomes uneven.

In addition, the plunger of the above-described structure is not directly connected to the gasket by a screw structure or the like, as in the case of the conventional plunger and gasket. Since the gasket is connected to the plunger main body portion via the connecting portion welded together at the contact surface, the assembling operation for directly connecting the plunger and the gasket can be omitted, and the occurrence of positional displacement of the gasket or shape deformation due to deformation during the assembling operation can be prevented.

In the above configuration, it is preferable that a plurality of grooves are radially or spirally formed on the tip end surface of the connecting portion with the concave portion as a center. For example, the molten resin supplied from a position facing the recess flows into the recess, and then flows through a groove portion provided radially or spirally around the recess, 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 situation in which the degree of fusion at the contact surface between the gasket and the connecting portion becomes uneven.

In the above configuration, it is preferable that a flange portion protruding outward in the radial direction be provided on a connection side of the connection portion with the plunger main body portion, and a diameter of the flange portion be substantially the same as a diameter of an outer peripheral surface of the gasket. By providing the flange portion having a diameter substantially equal to the diameter of the outer peripheral surface of the gasket at the connecting portion, when the syringe plunger of the present invention is housed in the outer cylinder of the syringe and combined together, the syringe plunger of the present invention can be slid in a state where the flange portion is in contact with the inner peripheral surface of the syringe. As a result, the syringe plunger of the present invention can be prevented from sliding while shaking, and the sliding property of the syringe plunger with respect to the syringe can be improved.

In the above-described configuration, it is preferable that the connecting portion has a female screw portion inside, the plunger main body portion has a male screw portion screwed with the female screw portion, and the connecting portion and the plunger main body portion are joined by a screwing structure. Unlike the conventional plunger and gasket, the plunger and the gasket are not directly connected by a screw structure or the like. The plunger body portion is engaged with a connecting portion, which is housed at least partially in the interior of the gasket, by screwing, and is provided integrally with the gasket by welding. That is, since the gasket is formed integrally 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 gasket can be prevented from being displaced, deformed, or deformed in shape. As a result, leakage of the chemical solution and incorporation of air bubbles can be prevented.

In the above configuration, the following structure may be adopted: the connecting portion has a main body portion having an annular stepped portion, a top portion provided at a front end of the main body portion, and an internal thread portion provided at a position of the main body portion on a rear end side of a position where the stepped portion is formed, and an inside of the connecting portion is hollow on the top side of the stepped portion by engagement of the plunger main body portion and the connecting portion by a screw structure.

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

In order to solve the above problems, a method of manufacturing a syringe plunger according to the present invention is a method of manufacturing a syringe plunger including: a plunger body portion; a connecting portion provided at a front end of the plunger body portion; and a gasket having a closed front end and an open rear end, and accommodating at least a part of the connecting portion from the rear end side, wherein the method for manufacturing a plunger for a syringe includes: a step of molding the connecting portion having a concave portion in a center portion of a tip surface thereof using a first mold having an inner surface shape for forming a tip shape and a side surface shape of the connecting portion and a common mold having an inner surface shape for forming an inner shape of the connecting portion; and a step of clamping the common mold with the connecting portion held therein, supplying a molten resin from a molten resin supply gate, filling the molten resin into a cavity, and cooling the filled molten resin to mold the gasket welded to the connecting portion at a contact surface including at least the recessed portion, wherein the second mold is capable of forming the cavity for molding the gasket when combined with the common mold, and the second mold includes the molten resin supply gate for supplying the molten resin toward the recessed portion at a position facing the recessed portion of the connecting portion.

In the above configuration, first, the connection portion is formed using the first mold and the common mold. The first mold has an inner surface shape for forming a tip shape and a side surface shape of the connecting portion, and particularly, the inner surface shape is set to: the front end shape of the connecting part is formed into a concave part at the center of the front end surface. The common mold has an inner surface shape for forming an inner shape of the connection portion.

Next, a second mold capable of forming a cavity for molding the gasket when combined with the common mold is prepared. The second mold includes a molten resin supply gate for supplying a molten resin toward the recess at a position facing the recess provided in the connecting portion. Then, the second mold and the common mold are clamped in a state in which the connecting portion is held therein, and the molten resin is supplied from the molten resin supply gate into the cavity formed thereby. Since the molten resin supply gate is provided at a position facing the concave portion of the connecting portion, the supplied molten resin flows into the concave portion first and then spreads throughout the cavity. Subsequently, the molten resin filled in the cavity is cooled, whereby the gasket is formed in a state of being welded to the connecting portion at the contact surface thereof. In this way, in the above-described structure, when the molten resin is supplied, the flow state is controlled so that the molten resin flows into the concave portion of the connecting portion first, thereby improving the case where the degree of fusion at the contact surface between the gasket and the connecting portion becomes uneven.

In the above-described manufacturing method, unlike the conventional plunger and gasket, the plunger and the gasket are not directly connected to each other by a screw structure or the like. Since the gasket is connected to the plunger main body portion via the connecting portion welded together at the contact surface, the manufacturing method of the structure can omit the assembly work for directly connecting the plunger and the gasket. Further, the plunger can be manufactured without causing positional displacement of the gasket and deformation of the shape due to deformation, which are caused when the assembling work is performed.

In the above configuration, it is preferable that a plurality of grooves are formed radially or spirally on the tip surface of the connection portion with the recess as a center. For example, the molten resin supplied from a position facing the recess first flows into the recess, and then flows through the groove portions radially provided around the recess, and spreads over the entire cavity. By guiding the flow direction of the molten resin in this manner, the degree of fusion at the contact surface between the gasket and the connecting portion can be further improved.

In the above structure, it is preferable that a resin obtained by melting a thermoplastic elastomer resin is used as the molten resin.

In order to solve the above problem, a medical syringe according to the present invention includes: the plunger for a syringe as described above; and an outer cylinder for syringe which slidably accommodates the gasket for syringe.

According to the above configuration, since the gasket is integrally provided with the connecting portion of the syringe plunger by welding, the gasket and the plunger can be prevented from being loosened or separated from each other during use. Further, for example, an assembly work for directly connecting the plunger for syringe and the gasket for covering the outer cylinder for syringe is not required. Therefore, the workability is improved, and the occurrence of leakage of the chemical liquid and the occurrence of air bubbles due to the positional displacement or deformation of the gasket which occurs during the assembly operation can be prevented.

Effects of the invention

According to the present invention, the gasket is integrally provided with the plunger at the joint portion thereof by welding, and the recess portion is provided at the center portion of the front end surface of the joint portion. Further, the recessed portion functions as a molten resin receiving portion for receiving molten resin for gasket molding supplied at the time of gasket molding, whereby in the present invention, it is possible to suppress the flow of the molten resin from becoming turbulent, and to improve the situation in which the degree of fusion at the contact surface between the gasket and the connecting portion becomes uneven.

As a result, for example, in the sterilization of a medical syringe using an autoclave or the like before and after the filling of a chemical solution, the occurrence of separation at the welded surface between the gasket and the connecting portion can be suppressed. Further, since the smoothness of the distal end surface of the gasket is not impaired by making the degree of welding uniform, the distal end surface of the gasket can be attached to the shape of the inner wall surface of the syringe outer tube which slidably accommodates the gasket with high accuracy. As a result, the medical syringe of the present invention can discharge the medical fluid filled in the syringe outer tube without leaving any residue. In addition, even if the medical syringe is installed at a position higher than the patient in a state where the medical syringe is filled with the medical fluid, the occurrence of detachment at the welded surface between the gasket and the connecting portion can be prevented. As a result, the occurrence of so-called siphon phenomenon in which the liquid medicine rapidly flows to the patient can be prevented. In addition, even when blood is returned to confirm that the patient has been properly punctured, the gasket can be prevented from being detached from the connecting portion.

Further, according to the present invention, since the gasket is formed in a structure in which at least a part of the connecting portion for connecting to the plunger main body portion is housed and is welded together at the contact surface with the connecting portion, it is possible to prevent the gasket and the plunger main body portion from being loosened or separated from each other in use or the like. Further, since the assembling work of directly connecting the plunger and the gasket as in the conventional plunger is not required in use, the workability is improved, and the occurrence of leakage of the chemical liquid and the occurrence of air bubbles due to the positional displacement or shape deformation of the gasket generated in the work can be prevented.

Drawings

Fig. 1 is a sectional view showing a medical prefilled syringe according to embodiment 1 of the present invention.

Fig. 2 is a side view showing a syringe plunger and a syringe outer cylinder of the medical prefilled syringe.

Fig. 3 is a schematic sectional view showing the syringe plunger.

Fig. 4 (a) is a schematic cross-sectional view showing a gasket of the syringe plunger and a connecting portion housed in the gasket, in which fig. b is a plan view showing a planar shape of the connecting portion, and fig. c is a plan view showing a planar shape of another connecting portion.

Fig. 5 (a) is a side view showing the gasket of the syringe plunger, fig. 5 (b) is a cross-sectional view showing the gasket, and fig. 5 (c) is a plan view showing the gasket.

Fig. 6 is a schematic sectional view showing a step of molding the connecting portion of the syringe plunger.

Fig. 7 is a schematic sectional view showing a step of forming a gasket of the syringe plunger.

Fig. 8 is a schematic cross-sectional view showing another connecting portion of the syringe plunger, in which (a) shows a case where a convex portion is provided at a position corresponding to a concave portion on an inner wall surface of the connecting portion, and (b) shows a case where the connecting portion does not include a flange portion.

Fig. 9 is a sectional view showing a syringe plunger of a medical prefilled syringe according to embodiment 2 of the present invention.

Fig. 10 (a) is a side view showing the packing and the connecting portion of the syringe plunger, fig. 10 (b) is a cross-sectional view showing the packing and the connecting portion, and fig. 10 (c) is a cross-sectional view showing the connecting portion.

Detailed Description

(embodiment mode 1)

[ medical syringes ]

As a medical syringe (hereinafter, referred to as "syringe") according to the present embodiment, a prefilled syringe will be described below as an example. Fig. 1 is a 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") of the syringe.

As shown in fig. 1 and 2, the syringe 10 of the present embodiment includes: an outer cylinder 11 having a nozzle 12 at a front end thereof; a cap 3 sealing the nozzle portion 12; a plunger 21 having a gasket 23 at a connection portion; and a chemical liquid 6 filled in a chamber formed by the outer tube 11, the cap 3, and the gasket 23.

The outer cylinder 11 includes: a cylindrical portion 13 formed substantially in a cylindrical shape; a nozzle section 12 provided at the front end of the cylindrical section 13; and a finger grip 14 provided at the rear end of the cylindrical portion 13. The length of the outer cylinder 11 is not particularly limited and may be appropriately set as needed.

The outer tube 11 is preferably made of a material exhibiting transparency or semi-transparency to the extent that at least the inside thereof can be visually confirmed, and more preferably made of a material having poor oxygen permeability or 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 cycloolefin 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 portion 13 is formed of a bottomed cylindrical member. The diameter and length of the cylindrical portion 13 are not particularly limited and may be appropriately set. A nozzle portion 12 that is constricted relative to the cylindrical body portion of the cylindrical portion 13 is integrally formed in the central portion of the bottom portion 15 of the cylindrical portion 13. The nozzle portion 12 is used by attaching a needle holder of a needle tube and a connector, not shown, for example.

The nozzle portion 12 is located at the center (central opening) of the cylindrical portion 13 in the cross-sectional direction of the cylindrical portion 13 (i.e., the direction perpendicular to the longitudinal direction of the cylindrical portion 13). However, the present embodiment is not limited to this, and may be provided at a position offset from the center (side port), for example. The diameter and height of the opening portion of the nozzle 12 are not particularly limited and may be appropriately set. Further, an annular wall 17 is provided around the nozzle portion 12 so as to be spaced apart by a predetermined distance. The height of the annular wall 17 is set to be lower than the height of the nozzle 12, and the nozzle 12 is set to protrude from the open front end of the annular wall 17. However, the present invention is not limited to this embodiment, and the annular wall 17 may not be provided. In order to hermetically seal the inner cavity of the nozzle portion 12, a cap 3 as a sealing member is detachably provided at the front end of the nozzle portion 12. The present embodiment is not limited to this embodiment, and for example, a sealing member made of a film or the like may be bonded.

The finger grip 14 protrudes radially outward from the cylindrical portion 13 and is integrally formed on the outer periphery of the base end of the outer tube 11. When the plunger 21 is operated to move relative to the outer cylinder 11, a finger is caught on the finger grip 14 and operated. In the case of using a known syringe pump, the finger grip 14 is fixed to the syringe pump, and the plunger 21 is operated to move 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. This makes it possible to grasp the amount of the chemical solution 6 in the syringe 10.

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

The plunger body 20 includes: a plunger shaft portion 22 having a cross-sectional shape; an external thread portion 43 provided in front of the plunger shaft portion 22; a packing pressing portion 25 provided at the rear end of the male screw portion 43; and a plunger pressing disk portion 26 provided at a rear end portion of the plunger shaft portion 22, wherein the plunger body portion 20 is formed of the same material and has an integral structure. The plunger body portion 20 and the connecting portion 24 are configured to be connectable by screwing the female screw portion 24c of the connecting portion 24 and the male screw portion 43 provided on the packing pressing portion 25. However, the present invention is not limited to this embodiment, and the plunger body 20 and the connecting portion 24 may be integrally formed of the same material.

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

As shown in fig. 4 (a) and 4 (b), the top portion 24a of the connecting portion 24 has a substantially conical shape, and the body portion 24b has a cylindrical shape. Fig. 4 (a) is a schematic cross-sectional view showing the connecting portion 24 housed in the gasket 23, and fig. 4 (b) is a plan view showing a planar shape of the connecting portion 24. By forming the top portion 24a in a substantially conical shape, the fluidity of the molten resin for gasket molding supplied at the time of molding the gasket 23 can be improved. The shape of the connecting portion 24 is not limited to the above-described form, and for example, the top portion 24a may be substantially polygonal pyramid-shaped, and the body portion 24b may be polygonal prism-shaped.

As shown in fig. 4 (b), a recess 27 is provided in the center of the front end surface of the connecting portion 24 (top portion 24 a). The recessed portion 27 functions as a molten resin receiving portion for receiving molten resin for gasket molding supplied at the time of molding the gasket 23. For example, when molten resin is supplied into the cavity for gasket molding from a position facing the concave portion, the molten resin flows into the concave portion 27 first with respect to the connecting portion 24, and then spreads and fills the entire cavity. By controlling the flow of the molten resin in this manner, it is possible to improve the unevenness of the degree of welding of the contact surface between the inner wall surface of the gasket 23 and the connection portion 24.

The opening of the recess 27 is substantially circular in plan view (see fig. 4 (b)). This prevents the molten resin for gasket molding from flowing in a specific direction after the molten resin is received in the recess 27. However, the opening shape of the recess 27 is not particularly limited as long as the recess 27 can be formed, and may be, for example, a rectangular shape, a polygonal shape, or the like. The diameter of the opening shape of the recess 27 is not particularly limited, and may be appropriately set as needed.

The depth shape of the recess 27 (cross-sectional shape of the recess 27 in cross section) is conical. This can improve the releasability of the molded connecting portion 24 from the mold. However, the depth 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. The bottom surface of the recess 27 may be rounded. The lower limit of the maximum depth of the recess 27 is preferably 0.1mm or more, more preferably 0.2mm or more, and particularly preferably 0.5mm or more. The upper limit of the maximum depth of the recess 27 is preferably 2mm or less, more preferably 1.5mm or less, and particularly preferably 1mm or less. By setting the lower limit of the maximum depth of the recess 27 to 0.1mm or more, the function as a molten resin receiving portion can be improved. On the other hand, by setting the upper limit value of the maximum depth of the recessed portion 27 to 2mm or less, it is possible to prevent the function of the recessed portion 27 as a 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 has flowed into the concave portion 27 first may stagnate, and as a result, solidification may start due to cooling, and the flow of the molten resin that is filled later may become turbulent. Therefore, by setting the depth of the recessed portion 27 to 2mm or less, the molten resin that initially flows into the recessed portion 27 can be prevented from staying, and the function of the recessed portion 27 as a molten resin receiving portion can be maintained.

The lower limit of the maximum thickness of the connecting portion 24 at the portion where the recess 27 is provided is preferably 0.2mm or more, and more preferably 1mm or more. On the other hand, the upper limit value of the maximum thickness of the connecting portion 24 is preferably 3mm or less, and more preferably 2mm or less. By setting the lower limit of the maximum thickness of the connecting portion 24 to 0.2mm or more, the volume of the cavity space can be secured, and the supplied molten resin can be made to flow. On the other hand, by setting the upper limit of the maximum thickness of the connecting portion 24 to 3mm or less, it is possible to suppress the cooling time of the molten resin from becoming long. Further, it is possible to prevent the occurrence of appearance defects and shape defects such as dents (recessed deformation of the surface due to molding shrinkage).

The body portion 24b of the connecting portion 24 is open at the rear end side, and a female screw portion 24c is provided inside thereof. This enables the external thread portion 43 provided in the packing pressing portion 25 to be screwed. The plunger 21 of the present embodiment is not directly connected to the gasket 23 by a screw structure or the like. The plunger body portion 20 is joined by screwing to a connecting portion 24 provided inside the gasket 23 by fusion at the contact surface. This prevents the gasket from being displaced, deformed, or deformed when the plunger and the gasket are directly connected to each other by a screw structure or the like, and as a result, prevents leakage of the chemical solution or mixing of air bubbles.

Further, a flange portion 28 is provided on the connection side of the connection portion 24 with the plunger body portion 20, that is, on the rear end side of the body portion 24 b. The flange portion 28 has an annular shape protruding radially outward from the main body portion 24 b. The diameter of the flange portion 28 is substantially the same as the diameter of the outer peripheral surface of the gasket 23, whereby 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 outer tube 11 housed in the syringe 10 is assembled, the plunger 21 can be slid in a state where the flange portion 28 is in contact with the inner peripheral surface of the syringe 10. As a result, the plunger 21 can be prevented from sliding while shaking, and the sliding property of the plunger 21 with respect to the outer tube 11 of the syringe 10 can be improved.

As shown in fig. 4c, a plurality of grooves 29 connected to the recess 27 may be provided on the tip surface of the connecting portion 24 (top portion 24a), and the plurality of grooves 29 may be provided radially about the recess 27. Thereby, the molten resin for gasket formation that has flowed into the recessed portion 27 can be guided by the groove portion 29 and radially flow from the recessed portion 27. As a result, the flow of the molten resin can be prevented from being turbulent. The number of the grooves 29 is not particularly limited and may be appropriately set as needed. The depth of the groove 29 (i.e., 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 of the groove 29 include a V-shape. The depth of the groove 29 is preferably the same as the depth of the recess 27. This can further reduce the occurrence of turbulent flow of the molten resin.

The grooves 29 are all the same length and extend from the recessed portion 27 to the peripheral edge at the top portion 24 a. The length of the groove 29 is not particularly limited, and may be set as appropriate according to the size of the apex 24a, and the like. For example, each groove 29 may extend further to the circumferential portion at the top portion 24 a. The lengths of the respective groove portions 29 in the extending direction may be different from each other. In this case, for example, the long groove portion and the short groove portion may be alternately arranged in the extending direction. This allows the molten resin to radially flow with a uniform flow amount around the recess 27.

The grooves 29 all extend to the same depth. The lower limit of the depth of the groove 29 is preferably 0.1mm or more, more preferably 0.2mm or more, and particularly preferably 0.5mm or more. The upper limit of the depth of the groove 29 is preferably 2mm or less, more preferably 1.5mm or less, and particularly preferably 1mm or less. By setting the lower limit of the depth of the groove portion 29 to 0.1mm or more, the function as a guide portion for the flowing molten resin can be maintained. On the other hand, by setting the upper limit value of the depth of the groove portion 29 to 2mm or less, it is possible to prevent the function of guiding the flow of the molten resin from being impaired. The depth of each groove 29 may be gradually reduced as it goes away from the recess 27 in the extending direction. The depth of each groove 29 may be different from each other. In this case, for example, deep grooves and shallow grooves may be alternately arranged in the extending direction. This allows the molten resin to radially flow with a uniform flow amount around the recess 27.

The width of the groove portion 29 (width in a direction perpendicular to the extending direction) is the same as the diameter of the recess 27, or is not particularly limited as long as it is smaller than the diameter. However, the groove portion 29 is preferably wide enough to allow the molten resin to flow from the center of the top portion 24a to the peripheral edge portion. The width of the groove 29 is the same from the peripheral edge of the concave portion 27 to the top, but the present invention is not limited thereto. For example, the width of the groove 29 may be gradually increased or decreased as it goes away from the recess 27 in the extending direction.

In addition, although the groove portions 29 of the present embodiment extend radially from the central recessed portion 27 to the peripheral edge portion at the top portion 24a, the present invention is not limited to this embodiment. For example, the center of the concave portion 27 may extend spirally. In this case, the flow path of the flowing molten resin can be extended, and thus the position where the molten resin stays can be reduced.

The material of the connecting portion 24 is not particularly limited, and examples thereof include hard or semi-hard resins such as high-density polyethylene, polypropylene, polystyrene, butadiene-styrene copolymer, acrylonitrile-butadiene-styrene copolymer, polymethylpentene, polycarbonate, acrylic resin, polyethylene terephthalate, and cyclic polyolefin. Examples of the material constituting the connection portion 24 include thermoplastic elastomer resins such as 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 thermoplastic elastomer resin, and a mixture thereof. When the material of the connecting portion 24 is selected from these materials, it is preferable to select a material that can make the hardness of the connecting portion 24 greater than the hardness of the gasket 23. The material of the connecting portion 24 may be the same as or different from the material of the plunger 21. When the hardness of the plunger 21 is considered, it is preferable to select a material having a hardness equal to or higher than that of the plunger 21 when selecting the material constituting the connecting portion 24.

As shown in fig. 1 and 2, the gasket 23 is housed so as to be slidable in the cylindrical portion 13 of the outer cylinder 11. As shown in fig. 5 (a) to 5 (c), the gasket 23 includes: a gasket main body portion 31 extending with substantially the same outer diameter; a sealing portion 33 at the front end of the gasket main body portion 31; and an opening 34 at the rear end of the gasket main body 31. In addition, the gasket 23 is solid. Fig. 5 (a) is a side view showing the gasket of the syringe plunger, fig. 5 (b) is a cross-sectional view showing the gasket, and fig. 5 (c) is a plan view showing the gasket. The opening 34 is provided in the gasket 23 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 that a gap is not formed therebetween as much as possible when the closing portion abuts against the inner wall surface of the bottom portion 15 of the outer cylinder 11. The connection portion 24 is accommodated in the opening portion 34 of the gasket, and the inner wall surface of the opening portion 34 and the connection portion 24 are welded to each other without a gap at the contact portion, thereby forming an integral structure. That is, the gasket 23 is an integral structure as a part of the plunger 21. In addition, a convex portion 36 is provided at a position corresponding to the concave portion 27 of the connection portion 24 on the inner wall surface of the gasket 23. In addition, the "fusion" means the following meaning: as described later, the surface of the connecting portion 24 in contact with the gasket 23 is melted by the heat of the molten resin injected when the gasket 23 is molded by injection molding or the like, and as a result, the gasket 23 and the connecting portion 24 are joined together at the contact surface thereof after the gasket 23 is molded.

Annular ribs 32 are provided between the gasket main body portion 31 and the closing portion 33, and at the rear end of the gasket main body portion 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 the sliding property 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 material can be used. Elastic materials are meant to have the following meanings: at least when the plunger 21 is housed in the outer cylinder 11, the annular rib 32 of the gasket 23 can be deformed to such an extent that it comes into liquid-tight contact with the inner wall surface of the cylindrical portion 13. More specifically, examples thereof include thermoplastic elastomer resins, polyolefin resins, fluorine resins, and polyester resins. As the thermoplastic elastomer resin, for example, 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 thermoplastic elastomer resin, and a mixture thereof are preferable.

Among these constituent materials, in the present embodiment, a styrene-based thermoplastic elastomer resin and a polyester-based thermoplastic elastomer resin are preferable. The polyester-based thermoplastic elastomer resin is excellent in weldability with the connecting portion 24 of the plunger 21, and can prevent detachment of the plunger 21, although it depends on the type of the material constituting the connecting portion 24. In addition, the polyester-based thermoplastic elastomer resin is also excellent in heat resistance and abrasion resistance, and therefore can be prevented from being thermally deformed during the sterilization treatment of the chemical solution. As a result, the occurrence of liquid leakage or the mixing of air bubbles into the chemical solution due to the thermal deformation can be prevented. As the polyester-based thermoplastic elastomer resin, commercially available products can be used. Examples of such commercially available products include Primalloy (registered trademark, manufactured by mitsubishi chemical corporation), Hytrel (registered trademark, manufactured by donnay dupont) and the like.

The surface of the seal gasket 23 may be coated with a lubricant. This can further improve the sliding property with respect to the inner wall surface of the cylindrical portion 13 of the outer cylinder 11. As the lubricant, there is no particular limitation, and for example, silicone oil or the like can be used.

The packing pressing portion 25 is disc-shaped and can press the packing 23 through the connecting portion 24 when the plunger 21 is relatively moved with respect to the outer tube 11. Further, since the gasket 23 is in contact with the peripheral edge portion of the gasket pressing portion 25, the gasket 23 can be directly pressed against the peripheral edge portion. The thickness of the packing pressing portion 25 is not particularly limited, and may be appropriately set as necessary. The diameter of the packing pressing portion 25 is only required to be sufficient to allow the plunger 21 to slide in the outer tube 11, and is set smaller than the inner diameter of the cylindrical portion 13 of the outer tube 11.

The disk portion 26 for plunger pressing is disk-shaped, and the thickness thereof is not particularly limited and may be appropriately set as necessary. The diameter of the disk portion 26 is not particularly limited, and may be set as appropriate as needed. Instead of the disk portion 26, a polygonal plate-shaped member may be used.

The medical fluid 6 is not particularly limited, and a conventionally known prefilled syringe preparation or the like can be preferably used.

[ method for producing plunger for syringe ]

Next, a method for manufacturing the plunger 21 according to the present embodiment will be described below with reference to fig. 6 and 7. Fig. 6 is a schematic sectional view showing a molding process of the connecting portion 24 of the plunger 21. Fig. 7 is a schematic sectional view showing a step of forming the gasket 23 of the plunger 21.

The method for manufacturing the plunger 21 of the present embodiment includes at least: a step of molding the connection portion 24 using a first mold and a common mold; and a step of molding the gasket 23 by using a second mold and a common mold so as to be welded to the connection portion 24 at the contact surface. In the present embodiment, the connection portion 24 and the gasket 23 are formed by a two-color forming method.

First, as shown in fig. 6 (a), in the step of molding the connection portion 24, a first mold 51 and a common mold 52 are prepared, the first mold 51 having an inner surface shape for forming the tip shape and the side surface shape of the connection portion 24, and the common mold 52 having an inner surface shape for forming the inner shape of the connection portion 24. The first mold 51 is a core (male mold), and the common mold 52 is a cavity (female mold). The first mold 51 and the common mold 52 have a structure in which a cavity capable of molding the connection portion 24 is formed when the molds are closed. The first mold 51 is provided with a convex portion 53 for forming a concave portion to form a concave portion 27 in the center of the front end surface of the formed connecting portion 24. 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 in the central portion of the first mold 51, but the present invention is not limited thereto. For example, the position of the first molten resin supply gate 54 can be set as appropriate so that the molten resin flows from a thick portion to a thin portion of the connection portion 24 to be formed.

As shown in fig. 6 (b), the first mold 51 and the common mold 52 are clamped, and then, as shown in fig. 6 (c), a molten resin 55 obtained by melting a resin that is a constituent material of the connecting portion 24 is injected into the cavity, thereby molding the connecting portion 24. The injection pressure of the molten resin is not particularly limited, and may be appropriately set as needed. The injected molten resin is cooled in a state of mold clamping. The cooling time is not particularly limited and may be appropriately set as needed. After the mold is opened, as shown in fig. 6 (d), the connecting portion 24 is formed in which the concave portion 27 is formed in the center portion of the front end surface and the female screw portion 24c is provided therein.

Next, the gasket 23 is molded (see fig. 7 a to 7 d). The molding of the gasket 23 is performed using the second mold 56 and the common mold 52. The gasket 23 is formed in a state where the connecting portion 24 is placed inside the second mold 56 and the common mold 52 after the mold closing. The second mold 56 is a core (male mold). The second mold 56 and the common mold 52 have a structure in which a cavity for molding the gasket 23 is formed when the molds are closed. The second mold 56 includes 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 concave portion 27 of the connecting portion 24 placed inside the second mold 56 and the common mold 52 after the mold clamping.

As shown in fig. 7 (b), the second mold 56 and the common mold 52 are closed, and then, as shown in fig. 7 (c), a molten resin 58 obtained by melting a resin that is a constituent material of the gasket 23 is injected into the cavity to mold the gasket 23. 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 flows into the concave portion 27 first, and then spreads throughout the cavity. This can improve the unevenness of the degree of welding at the contact surface between the gasket 23 and the connecting portion 24.

The injection pressure of the molten resin 58 is not particularly limited, and may be appropriately set as needed. The filling speed of the molten resin 58 (speed from the injection of the molten resin 58 into the cavity to the completion of filling) is not particularly limited, and may be set as appropriate in accordance with the injection pressure or the like. After the injection of the molten resin 58, a pressure holding step of applying pressure to the molten resin 58 to compress the molten resin 58 (pressure control) in order to compensate for the cooling shrinkage amount of the molten resin 58 may be performed. After that, the injected molten resin 58 is cooled in a state of mold clamping. The cooling time is not particularly limited and may be appropriately set as needed. After the mold is opened, as shown in fig. 7 (d), the gasket 23 is formed with its front end closed and the connection portion 24 is accommodated from the opening 34 at the rear end. The inner wall surface of the gasket 23 is welded to the contact surface including the recess 27 of the connecting portion 24.

The method of taking out the molded gasket 23 and the molded connecting portion 24 from the common mold 52 is not particularly limited, and various methods of rotational demolding may be employed. Specifically, for example, a motor rack system, a rack and pinion system (using a mold opening and closing motion), a forced mold release system, a split slide system, and the like can be given. The motor rack mode is as follows: a motor is used as a power source for transmitting rotation to a screw core for forming the female screw portion 24c in the inner wall surface of the connecting portion 24. In addition, the rack and pinion system is: the opening and closing movement of the molding machine is transmitted by a rack and a gear to rotate the screw core. The forced demoulding mode is as follows: the molded gasket 23 and the connecting portion 24 are forcibly taken out from the common mold 52. The split internal sliding mode comprises the following steps: the method of easily performing mold release by dividing the threaded core into a plurality of parts after molding. Among these systems, the motor-rack system, the rack-and-pinion system (using mold opening and closing movements), and the divided sliding system are preferable from the viewpoint of being able to increase the thread pitch of the female screw portion 24c and to make the screw structure with the male screw portion 43 provided in the plunger body portion 20 firm. Further, among these systems, the motor-rack system is particularly preferable from the viewpoint of suppressing the facility cost.

On the other hand, the plunger body 20 may be manufactured by a known molding method. Specifically, for example, injection molding and the like can be given. Thereafter, the plunger 21 according to the present embodiment can be manufactured by screwing the external thread portion 43 of the plunger body portion 20 into the internal thread portion 24c of the coupling portion 24 to connect the plunger body portion 20 and the coupling portion 24.

[ other items ]

As for the structure of the gasket and the connecting portion housed in the gasket, the structure shown in fig. 8 (a) or fig. 8 (b) may be adopted in the present embodiment. Fig. 8 is a schematic cross-sectional view showing another connecting portion, in which (a) shows a case where a convex portion is provided at a position corresponding to a concave portion on an inner wall surface of the connecting portion, and (b) shows a case where the connecting portion does not include a flange portion.

As shown in fig. 8 (a), the connecting portion 24 'is flat without a top portion at the tip, and the connecting portion 24' is formed of a cylindrical body portion 24 b. Since the connecting portion 24' does not have a substantially conical top portion, the gasket 23 is thick. A recess 27 is provided in the center of the tip end surface of the connecting portion 24 ', and a projection 37 is further provided in a position corresponding to the recess 27 on the inner wall surface of the connecting portion 24' in the structure shown in fig. 8. The convex portion 37 corresponds to the concave portion 27. Therefore, 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, a rectangular shape, a polygonal shape, or the like can be adopted. 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 a plan view is also 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 center portion of the tip end surface provided with the concave portion 27 can be made the same as that of the other portions. As a result, the decrease in mechanical strength of the center portion of the distal end surface of the connecting portion 24' can be suppressed.

As shown in fig. 8 (b), the connecting portion 24 ″ has a structure that does not include the flange portion 28 in comparison with the connecting portion 24, and the connecting portion 24 ″ is entirely housed inside the gasket 23.

(embodiment mode 2)

Embodiment 2 of the present invention will be described below with reference to fig. 9 and 10. Note that members having the same functions as those in embodiment 1 are given the same reference numerals, and description thereof is omitted. Fig. 9 is a sectional view showing a syringe plunger of the medical prefilled syringe according to embodiment 2. Fig. 10 (a) is a side view showing the gasket and the connecting portion of the syringe plunger, fig. 10 (b) is a cross-sectional view showing the gasket and the connecting portion, and fig. 10 (c) is a cross-sectional view showing the connecting portion.

Embodiment 2 is common to embodiment 1 in that the gasket 23 is integrally provided by welding to the connection portion 61, as shown in fig. 9 and 10. The structure in which the plunger 21 and the coupling portion 61 are connectable to and separable from each other by screwing the female screw portion 24c provided in the coupling portion 61 and the male screw portion 43 provided in the packing pressing portion 25 is also common to embodiment 1. However, embodiment 2 is different from embodiment 1 in the structure of the connection portion 61.

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

An internal thread portion 24c that can be screwed into the external thread portion 43 provided in front of the plunger shaft portion 22 is provided on an inner wall surface of the lower portion 62b of the body portion 62. Therefore, when the plunger body portion 20 is connected to the connecting portion 61 by screwing the male screw portion 43 and the female screw portion 24c, the space 64 is formed in 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 62a of the body portion 62 housed inside the gasket 23 can be reduced. Thus, since the upper portion 62a can be compressively deformed, workability when the plunger 21 is housed in the outer tube 11 of the syringe 10 and assembled can be improved. The thickness of the upper portion 62a is preferably in the range of 0.2mm to 1.5mm, and more preferably in the range of 0.3mm to 1.5 mm. By setting the thickness of the upper portion 62a to 0.2mm or more, molding failure of the upper portion 62a can be prevented, and shape stability can be ensured. On the other hand, by setting the thickness of the upper portion 62a to 1.5mm or less, it is possible to prevent the compression deformation from becoming difficult, although it depends on the material of the connecting portion 61.

The connection portion (not shown) may be: the overall shape is a flat shape having no top at the front end, and is constituted only by the main body portion 62. In this case, the connecting portion does not have a substantially conical top portion, so that the gasket 23 is thick. In addition, a convex portion is provided at a position corresponding to the concave portion 27 on the inner wall surface of the connecting portion. This makes it possible to make the thickness of the center portion of the distal end surface provided with the recess 27 the same as that of the other portions. As a result, the decrease in mechanical strength of the center portion of the front end surface of the connecting portion can be suppressed.

(other items)

In embodiments 1 and 2, the case where the plunger main body portion and the connecting portion are connected by the screw structure has been described as an example, but the present invention is not limited to this embodiment. For example, the plunger body and the connecting portion may be connected to each other by a fitting structure. In this case, for example, a convex portion is provided in the plunger body portion, and a concave portion capable of fitting with the convex portion is provided in the connecting portion.

In embodiments 1 and 2, the case of a prefilled syringe has been described as an example, but the present invention is not limited to these embodiments. For example, the present invention can be applied to a syringe for blood collection, a syringe for air bag, a general syringe for test, and the like.

Description of the symbols

10 (for medical use) syringe

11 (for syringe) outer cylinder

12 nozzle part

13 cylindrical part

14 finger grip

15 bottom part

17 annular wall

20 plunger body part

21 plunger for syringe

22 plunger shaft part

23 sealing gasket

24 connecting part

24 main body part

24a top

24b main body part

24c internal thread part

25 sealing gasket pressing part

26 disc part

27 recess

28 flange part

29 groove part

31 gasket body part

32 annular Ribs

33 closure part

34 opening part

36. 37 convex part

43 external screw thread part

51 mould

52 common die

53 convex part for forming concave part

54 first molten resin supply gate

55 molten resin

56 mould

57 second molten resin supply gate

58 molten resin

61 connecting part

62 body portion

62a upper part

62b lower part

63 step part

64 space

Claims

1. A plunger for a syringe is provided with:

a plunger body portion;

a connecting portion provided at a front end of the plunger body portion; and

a gasket having a closed front end and an open rear end, and accommodating at least a part of the connection portion from the rear end side,

wherein a recess is provided at a central portion of a front end surface of the connecting portion,

the recessed portion is a molten resin receiving portion for receiving a molten resin for gasket molding supplied at the time of gasket molding,

the gasket and the connecting portion are welded together at a contact surface including at least the recess.

2. The plunger for a syringe according to claim 1,

the front end surface of the connecting portion is provided with a plurality of grooves radially or spirally around the recess.

3. The plunger for a syringe according to claim 1,

a flange portion protruding radially outward is provided on a connection side of the connection portion with the plunger body portion,

the diameter of the flange portion is substantially the same as the diameter of the outer peripheral surface of the gasket.

4. The plunger for a syringe according to claim 1,

the connecting portion has a female screw portion therein, the plunger body portion has a male screw portion to be screwed with the female screw portion,

the connecting portion is engaged with the plunger main body portion by a screw engagement structure.

5. The plunger for a syringe according to claim 4,

the connecting part has a main body part and a top part, the main body part is provided with an annular step part, the top part is arranged at the front end of the main body part,

the female screw portion is provided on the rear end side of the body portion with respect to the formation position of the stepped portion,

the interior of the connecting portion is hollow on the top side of the stepped portion by engagement of the plunger body portion and the connecting portion by a screw structure.

6. The plunger for a syringe according to claim 1,

the gasket is made of a thermoplastic elastomer resin.

7. A method for manufacturing a plunger for a syringe, wherein,

the plunger for syringe is provided with:

a plunger body portion;

a connecting portion provided at a front end of the plunger body portion; and

the manufacturing method of the plunger for the syringe comprises the following steps:

a step of forming the connecting portion having a concave portion in a center portion of a front end surface thereof by using a first mold having an inner surface shape for forming a front end shape and a side surface shape of the connecting portion and a common mold having an inner surface shape for forming an inner side shape of the connecting portion; and

and a step of clamping the common mold with the connecting portion held therein, supplying a molten resin from a molten resin supply gate, filling the molten resin into a cavity, and cooling the filled molten resin to mold the gasket welded to the connecting portion at a contact surface including at least the recessed portion, wherein the second mold is capable of forming the cavity for molding the gasket when combined with the common mold, and the second mold includes the molten resin supply gate for supplying the molten resin toward the recessed portion at a position facing the recessed portion of the connecting portion.

8. The method of manufacturing a plunger for a syringe according to claim 7,

a plurality of grooves are formed radially or spirally on the front end surface of the connecting portion with the concave portion as a center.

9. The method of manufacturing a plunger for a syringe according to claim 7,

as the molten resin, a resin obtained by melting a thermoplastic elastomer resin is used.

10. A medical syringe is provided with:

the plunger for a syringe according to any one of claims 1 to 6; and

and an outer cylinder for the syringe, which slidably accommodates the gasket for the syringe.