Patent Description:
There has been conventionally proposed a gasket exerting high safety and high sealing performance over a long period of time, with a medical solution being injected therein (see e.g., Publication of Japanese Translation of PCT International Application No. <CIT>).

As shown in <FIG>, a gasket <NUM> disclosed in Publication of Japanese Translation of PCT International Application No. <CIT> mainly includes a gasket body <NUM>, composed of a plunger section <NUM> and a seal section <NUM>, and an inert film <NUM> laminated on the surface of the plunger section <NUM> of the gasket body <NUM>.

The inert film <NUM> exerts high resistance against medical solution and is thus laminated on the plunger section <NUM> of the gasket body <NUM>, whereby the gasket <NUM> per se can be enhanced in resistance against medical solution.

In spite of the advantage described above, the well-known gasket <NUM> has had a drawback as follows. When a certain time elapses after setting the gasket <NUM> in a syringe <NUM> in which a medical solution <NUM> is encapsulated, the medical solution <NUM> seeps through the inert film <NUM> and leaks out as shown in <FIG> and <FIG>. This occurs due to a structure that a cut surface <NUM> of the inert film <NUM> is located on the lateral surface of the gasket <NUM>.

As a reason for the drawback, it has been found that a large number of fine closed cells are formed inside and on the surface of a polytetrafluoroethylene (PTFE) film used as the inert film <NUM> (e.g., <CIT>). The PTFE film is stretched to a great extent, when adhered to the surface of the plunger section <NUM> of the gasket body <NUM>. Undesirably, the closed cells are connected to each other in alignment, whereby fine "pathways" (communicating holes) are formed. The medical solution <NUM> (especially, a surfactant-containing medical solution having become popular in recent years) gradually penetrates the pathways, and as a result, seeps therethrough and leaks out (see a leaking-out route "A" in <FIG> and <FIG>).

Furthermore, according to a manufacturing procedure of the gasket <NUM> disclosed in Publication of Japanese Translation of PCT International Application No. <CIT>, the inert film <NUM> is configured to be cut after molding the gasket body <NUM>, whereby the cut surface <NUM> of the inert film <NUM> is exposed to the lateral surface of the gasket <NUM>. Because of this, when permeating into the inert film <NUM> due to the reason described above, the medical solution <NUM> could leak out in large amount from the cut surface <NUM> through the communicating holes described above (see a leaking-out route "B" in <FIG> and <FIG>).

The present invention has been developed in view of the drawback of the prior arts described above. Hence, it is a main object of the present invention to provide a gasket, by which undesirable leakage of a medical solution is unlikely to occur, for instance, when the gasket is set in a syringe pre-filled with the medical solution and contacts the medical solution over a long period of time, a syringe including the gasket, and a method of manufacturing the gasket.

<CIT> discloses a gasket for glass or resin syringes which is laminated with an inert resin film and is excellent in plugging properties, liquid-tightness, and slidability. The gasket laminated with an inert resin film has multiple circular ribs that are to be in sliding contact with an inner wall of a syringe barrel, wherein the circular ribs include a front circular rib having a sliding contact portion whose cross section has a diameter that expands substantially linearly toward a back end of the syringe barrel, the linear portion has a length of <NUM> to <NUM>% of the length of a sliding side face of the gasket, and the diameter of the linear portion which expands substantially linearly toward a back end of the syringe barrel has a diameter expansion ratio X between a minimum diameter r (mm) and a maximum diameter R (mm) of <NUM> to <NUM>%.

<CIT> discloses a gasket comprising a distal, first molded part <NUM> containing a drug-contact surface and a first cyclic sliding surface which is adjacent to this, and a proximal, second molded parts <NUM> containing a plurality of cyclic sliding surfaces and formed by insert molding of the first molded part <NUM>. The lateral surface containing the drug-contact surface and the first cyclic sliding surface of the first molded part <NUM> is laminated with a synthetic resin film, and the end surface of the film laminated on the lateral surface of the first molded part <NUM> is implanted in the second molded part <NUM>.

<CIT> discloses a method for producing a prefilled syringe gasket, which ensures that a sliding portion of the gasket (a portion of the gasket to be kept in contact with a syringe barrel) is substantially free from a scratch or an existing scratch of the gasket is substantially eliminated. The prefilled syringe gasket includes a liquid contact portion, and a sliding portion to be kept in contact with an inner surface of a syringe barrel. The method includes the steps of: forming the gasket; and rubbing a surface of the sliding portion of the formed gasket against a predetermined base, wherein a rubbing direction in which the surface of the sliding portion is rubbed in the rubbing step extends circumferentially of the sliding portion.

<CIT> discloses a gasket device for use in a pre-filled syringe having a cylinder for containing liquid drug in sealing tightness. The liquid drug is pressurized by moving a plunger in the cylinder. The gasket device includes a gasket body, having resiliency, and movable toward the liquid drug with a front end of the plunger. A laminate layer is formed from PTFE (polytetrafluoroethylene), and disposed to cover a surface of the gasket body. The laminate layer includes a sealing portion, having a thickness Da, for sliding on an inner surface of the cylinder in sealing tightness. A liquid receiving portion has a thickness Db, for contacting the liquid drug in the cylinder. The thickness Da is from <NUM> microns to <NUM> microns. The thickness Db is from <NUM> microns to <NUM> microns. A ratio R1 of the thickness Db to the thickness Da is from <NUM> to <NUM>.

<CIT> discloses a method of manufacturing a sealing element for use in a fluid conveyance device comprising the steps of: forming an elastomeric sealing body including a first body portion defining at least one annular sealing rib, and a second body portion arranged on an end of the first body portion, the second body portion comprising an annular protrusion extending radially beyond the first body portion; and forming a layer of barrier material on a free end of the second body portion, wherein the forming steps are carried out in a single molding operation.

<CIT>discloses a gasket optimized for a pre-filled syringe, which has high sliding performance on a cylinder by using a sliding film, deals with a problem of an existing gasket main body formed of isobutylene-isoprene rubber by using a gasket main body formed of silicon rubber, and minimizes a concern that a liquid medicine in the cylinder (or moisture in the liquid medicine) may be dissipated to outside air and deals with a problem caused by permeability of the silicon rubber by covering a rear side of the gasket main body (an inner side surface of a concavity, and a rear-side circumferential edge portion near the concavity) with a non-permeable plastic base body and a flange portion.

The invention is defined by the subject-matter of independent claims <NUM>, <NUM> and <NUM>.

According to an aspect of the present invention, a gasket is provided that includes the features of claim <NUM>.

Preferably, the circumferential end surface of the PTFE film is made sealed by the gasket body.

Preferably, the circumferential end portion of the PTFE film attached to the solution contact surface of the gasket body has an extension ratio of less than or equal to <NUM>%.

Preferably, the gasket body is made of silicone rubber provided with slidability.

According to yet another aspect of the present invention, it is intended to provide a syringe that includes the gasket configured as any of the above, a medical solution, a syringe barrel, and a plunger rod.

According to further yet another aspect of the present invention, a method of manufacturing a gasket is provided that includes the features of claim 6Accordingly, a circumferential end portion of the PTFE film is curved to cover a circumferential edge of the solution contact surface, while a circumferential end surface of the PTFE film is buried in the slide contact portion of the gasket body so as not to be exposed to outside and is made sealed by the gasket body.

According to still further yet another aspect of the present invention, a method of manufacturing a gasket is provided that includes the features of claim <NUM> Accordingly, a circumferential end portion of the PTFE film is curved to cover a circumferential edge of the slide contact portion, while a circumferential end surface of the PTFE film faces in surface contact with a lateral surface of the gasket body and is made sealed by the gasket body.

According to the gasket of the present invention, the circumferential end portion of the PTFE film is curved toward the slide contact portion of the gasket body, and the circumferential end surface of the PTFE film is buried in the slide contact portion of the gasket so as not to be exposed to the outside. Thus, the circumferential end surface of the PTFE film is not exposed to the outside, whereby it is possible to prevent occurrence of an undesirable situation that a medical solution penetrates the PTFE film and leaks out from the circumferential end surface thereof through communicating holes and this situation brings about leakage of the medical solution from the gasket. Furthermore, when the circumferential end surface is made sealed by the gasket body, it is possible to increase as much as possible the possibilities of preventing leakage of the medical solution from the gasket.

Accordingly, it is possible to provide a gasket, by which undesirable leakage of a medical solution is unlikely to occur, for instance, when the gasket is set in a syringe pre-filled with the medical solution and contacts the medical solution over a long period of time, a syringe including the gasket, and a method of manufacturing the gasket.

Referring now to the attached drawings which form a part of this original disclosure:.

A gasket <NUM>, to which the present invention is applied, and a syringe <NUM> including the gasket <NUM> will be explained along with a practical example shown in drawings.

As shown in <FIG>, the syringe <NUM> mainly includes the gasket <NUM>, a medical solution <NUM>, a syringe barrel <NUM>, a plunger rod <NUM>, and a top cap <NUM>.

As shown in <FIG>, the gasket <NUM> mainly includes a gasket body <NUM> and a polytetrafluoroethylene (PTFE) film <NUM>.

The gasket body <NUM> has an approximately columnar shape. As shown in <FIG>, the gasket body <NUM> includes a solution contact portion <NUM>, a slide contact portion <NUM>, and a small diameter portion <NUM>. The solution contact portion <NUM> has a tip surface (referred to as "a solution contact surface <NUM>" in the specification of the present application) that contacts the medical solution <NUM> when the gasket body <NUM> is fitted into the syringe barrel <NUM>. The slide contact portion <NUM> is shaped in continuation to the solution contact portion <NUM> and has a diameter slightly greater than a diameter (inner diameter) of an inner surface <NUM> of the syringe barrel <NUM> into which the gasket <NUM> is fitted. The small diameter portion <NUM> is shaped in continuation to the slide contact portion <NUM> and is reduced in diameter to much extent than the slide contact portion <NUM>.

Besides, the gasket body <NUM> is provided with a female threaded hole <NUM> in a rear end surface <NUM> thereof. The plunger rod <NUM> is attached to the female threaded hole <NUM>.

A variety of elastomers (e.g., butyl rubber or silicone rubber) is usable as a material of which the gasket body <NUM> is made.

It should be noted that in use of a vulcanized molded rubber such as a butyl rubber, a silicone oil is required to be applied to the inner surface <NUM> of the syringe barrel <NUM> because of a slidability-related problem. Hence, it is preferred to use "silicone rubber" provided with slidability as the material of which the gasket body <NUM> is made.

"Silicone rubber" is a thermosetting elastomer, and for instance, uses "organopolysiloxane" in a liquid, grease, or clay state as a raw material thereof. "Organopolysiloxane" is a material that a methyl, vinyl, phenyl, or trifluoropropyl group is incorporated in a molecule, and which group should be incorporated in a molecule depends on requirements for special properties.

There exists plural types of "silicone rubber". Although any type of "silicone rubber" is usable in the present practical example, a peroxide crosslinked silicone rubber is herein used as an example. The peroxide crosslinked silicone rubber is formed by preparing liquid or grease "organopolysiloxane" that a vinyl group is incorporated in a molecule, adding thereto a necessary filling and a peroxide curing agent and then kneading the whole. Alternatively, an addition reaction silicone rubber can be exemplified. The addition reaction silicone rubber is formed by heating and curing two types of clay polysiloxane through chemical reactions using an organometallic compound of platinum, rhodium, tin, or so forth as a catalyst. One type of clay polysiloxane contains a vinyl group incorporated in a molecule, whereas the other type contains reactive hydrogen incorporated in the terminal of a molecule.

The silicone rubber provided with slidability is formed by, for instance, adding a peroxide functioning as a crosslinking agent to the liquid, grease, or clay organosiloxane prepared as a material (alternatively, adding a curing catalyst to the two types of clay polysiloxane described above), then adding thereto a predetermined amount of silicone oil, and kneading the whole with a kneader. Furthermore, a silica fine powder is added to the kneaded material by an appropriate amount (e.g., <NUM>%) to adjust the hardness of the kneaded material on an as-needed basis. If still necessary, for example, an ultrahigh molecular weight polyethylene (PE) fine powder is added thereto by a predetermined amount.

A PE resin, forming fine particles of the fine powder, is an ultrahigh molecular weight resin (the average molecular weight thereof is, for instance, <NUM> to <NUM> million or greater and may reach <NUM> million). Such ultrahigh molecular weight particles are not permeable to water, and besides, do not adhere to almost anything. Moreover, the molecular weight of the ultrahigh molecular weight PE is too high; hence, the ultrahigh molecular weight PE does not melt even at a high temperature and is kept in a spherical form even when molded at a high pressure. The surface of the spherical ultrahigh molecular weight PE is relatively smooth but is in part observed as uneven. The particle diameter of the spherical ultrahigh molecular weight fine particles contained in the fine powder falls in a range of <NUM> to <NUM>. More preferably, the particle diameter falls in a range of <NUM> to <NUM>. The ultrahigh molecular weight fine particles herein used have an average particle diameter of 25pm, <NUM>, or so forth, albeit depending on the grade thereof. When the particle size distribution of the ultrahigh molecular weight fine particles is wide, small diameter particles enter between large diameter particles and fill the gaps between the large diameter particles, whereby a close-packed state is realized. Now that the close-packed state is realized, the fine particles become impermeable to water. Hence, even if a water permeable silicone rubber base material or silicone oil is used, a medical use slidable silicone rubber of the present invention as a whole is supposed to exert quite low water permeability.

The silica fine powder is a type of powder using silica sand as a raw material and is mostly made of silica (SiO<NUM>). The silica fine powder is added to an elastic material to adjust the hardness thereof.

A method of molding the gasket body <NUM> will be exemplified. A compression mold, enabling molding of the gasket body <NUM>, is heated to an appropriate temperature. The PTFE film <NUM> is put between blocks of the mold, and the molding material described above (the silicone rubber formed by adding the silica powder, the silicone oil, and on an as-needed basis, the ultrahigh molecular weight PE powder to the raw material and then kneading the whole) is filled in the mold. In this condition, the mold is tightened and then heated and pressurized along with a predetermined procedure. Accordingly, thermal crosslinking advances in <NUM> to <NUM> minutes, whereby the gasket body <NUM> is obtained as an intended object. It should be noted that the gasket body <NUM> herein obtained is preferably subjected to secondary thermal treatment (annealing).

Next, the PTFE film <NUM> will be explained. As shown in <FIG>, the PTFE film <NUM> is arranged and set to cover the solution contact surface <NUM> of the solution contact portion <NUM> of the gasket body <NUM>. A circumferential end portion <NUM> of the PTFE film <NUM> is curved toward the slide contact portion <NUM> of the gasket body <NUM>, whereby a circumferential end surface <NUM> of the PTFE film <NUM> is buried in the slide contact portion <NUM> of the gasket body <NUM> so as not to be exposed to the outside.

Pure PTFE may be used as the material of the PTFE film <NUM> in the present practical example. However, it is more preferred to use, for instance, modified PTFE mixed with <NUM> to <NUM>% by mass of a fluorine resin (polytetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (abbreviated as PFA), tetrafluoroethylene-hexafluoropropylene copolymer, etc.) functioning as a crystallization inhibitor for PTFE. This is because the PTFE film <NUM> is provided with elasticity when made of the modified PTFE.

Besides, not only the pure or modified PTFE described above but also a type of PTFE manufactured with "skived method" may be used as the PTFE film <NUM> in the present practical example. In the skived method, a sheet of PTFE is obtained by cutting a PTFE block (round bar) in which closed cells are formed by hot isostatic pressing called HIP treatment.

A primary sintered block of PTFE is obtained by compression-molding a powder of the pure or modified PTFE and then sintering the compression-molded powder. In this sintering, the particles of the powder are in close contact with each other at contact portions thereof; however, when the sintered block of PTFE is viewed as a whole, ultrafine gaps are produced between non-contact portions of the powder particles and continue to each other, whereby a minute fluid is enabled to pass therethrough.

Alternatively, "cast method" may be employed as another method of manufacturing the PTFE film <NUM>. In the cast method, a sheet of PTFE is obtained by applying an emulsion of PTFE to the surface of a flat board so as to form a film thereon and then heating the film.

Referring back to <FIG>, the syringe barrel <NUM> is a cylindrical container and is provided with an attached portion <NUM> and a flange portion <NUM>. The attached portion <NUM> protrudes from the front end (tip) of a barrel body <NUM> and enables a syringe needle (not shown in the drawing) to be attached thereto. The flange portion <NUM> is a finger-hooked portion provided on the rear end of the barrel body <NUM>. Not only glass but also a hard resin (e.g., cyclo olefin polymer (COP), polypropylene (PP), ethylene norbornene copolymer (COC), etc.) is used as the material of the syringe barrel <NUM>. As described below, the gasket <NUM> according to the present practical example can keep high the watertightness of the syringe barrel <NUM> due to the structural feature thereof. Hence, a glass syringe barrel is also usable as the syringe barrel <NUM>, albeit inferior to a resin syringe barrel in dimensional accuracy of the inner diameter.

The plunger rod <NUM> is a rod-shaped member. The plunger rod <NUM> is provided with a male threaded portion <NUM> on the front end (tip) thereof, while being provided with a finger pushing portion <NUM> on the rear end thereof. The male threaded portion <NUM> of the plunger rod <NUM> is shaped as a male threaded screw enabled to be screwed and fitted into the female threaded hole <NUM> provided in the gasket body <NUM> of the gasket <NUM>. It should be noted that a resin such as cyclic polyolefin, polycarbonate, or polypropylene can be used as the material of the plunger rod <NUM>.

The top cap <NUM> includes a cap body <NUM> made in shape of a conical frustum and a cap flange portion <NUM> laterally extending in a disc shape from the edge of the top surface of the cap body <NUM>. The cap body <NUM> is provided with a recess <NUM> into which the attached portion <NUM> of the syringe barrel <NUM> is fitted. Besides, the top cap <NUM> may be made of an elastomer and a medical solution resistance film (of PTFE or PFA) may be laminated on the inner peripheral surface thereof. Here, the elastomer refers to a vulcanized rubber, a thermosetting elastomer, or a thermoplastic elastomer.

Next, a manufacturing procedure of the gasket <NUM> according to the present preferred embodiment will be explained. First, a mold <NUM> to be used for manufacturing the gasket <NUM> will be explained.

For example, as shown in <FIG>, the mold <NUM> is roughly divided into three blocks (a first block <NUM>, a second block <NUM>, and a third block <NUM>). The first block <NUM> is provided with plural pairs of a piston <NUM> and a male threaded screw <NUM> corresponding to the female threaded hole <NUM> formed in the gasket body <NUM>. Each pair of the piston <NUM> and the male threaded screw <NUM> protrudes downward from a first parting surface <NUM> located on the lower surface of a first block body <NUM> of the first block <NUM>. First, the piston <NUM> is formed to protrude from the first parting surface <NUM>, and then, the male threaded screw <NUM> is formed to protrude from the lower end of the piston <NUM>.

The second block <NUM> is provided with plural molding elastomer block fitting holes <NUM> in a second block body <NUM> thereof. The molding elastomer block fitting holes <NUM> penetrate the second block body <NUM> from a second upper parting surface <NUM> thereof located on the upper side in <FIG> to a second lower parting surface <NUM> thereof located on the lower side in <FIG>. The molding elastomer block fitting holes <NUM> are holes into which plural molding elastomer blocks <NUM> to be molded into plural gasket bodies <NUM> are fitted. It should be noted that each molding elastomer block <NUM> is fitted into each molding elastomer block fitting hole <NUM> such that the solution contact portion <NUM> of the gasket body <NUM> obtained by molding each molding elastomer block <NUM> faces downward in <FIG>.

Besides, each molding elastomer block fitting hole <NUM> is provided with a cutting portion <NUM> on a second lower parting surface <NUM>-side end thereof. The cutting portion <NUM> faces the third block <NUM>. As described below, an uncut PTFE film <NUM> is configured to be cut between the cutting portion <NUM> and the third block <NUM>.

Moreover, the second upper parting surface <NUM> is provided with plural springs <NUM> protruding toward the first block <NUM>.

The third block <NUM> is provided with plural molding recesses <NUM> on a third parting surface <NUM> of a third block body <NUM> thereof. The third parting surface <NUM> is joined to the second lower parting surface <NUM> of the second block <NUM>. Each molding recess <NUM> corresponds to the solution contact surface <NUM> of the solution contact portion <NUM> composing the gasket body <NUM> together with the slide contact portion <NUM>.

The mold <NUM> described above is prepared and the uncut PTFE film <NUM>, having a greater width than the aligned molding recesses <NUM>, is arranged and set with respect to the molding recesses <NUM>. Along with this, the molding elastomer blocks <NUM> are preliminarily fitted into the molding elastomer block fitting holes <NUM> of the second block <NUM>, respectively.

It should be noted that "adhesiveness improving treatment" is required to be performed in advance for a surface of the uncut PTFE film <NUM> (the upper surface thereof in <FIG>) that contacts each unmolded gasket body <NUM>. This is because in general, the uncut PTFE film <NUM> is hardly adhesive and exerts a quite weak adhesive force when adhered to a vulcanized molded rubber, a thermoplastic elastomer, or so forth. This is also true of when the material of each unmolded gasket body <NUM> is the vulcanized molded rubber, the thermoplastic elastomer, or so forth as well as when the material of each unmolded gasket body <NUM> is "silicone rubber" described above.

Specifically, "adhesiveness improving treatment" can be exemplified by a method of disposing a silica fine particle layer on a joint surface between the uncut PTFE film <NUM> and each unmolded gasket body <NUM>, chemical treatment with metallic sodium, plasma treatment performed in an argon atmosphere, or so forth. Furthermore, a mixture gas of oxygen and an easily available <NUM>, <NUM>-butadiene or <NUM>, <NUM>-butadiene gas may be introduced into a vacuum chamber in which the uncut PTFE film <NUM> is arranged and set, and subsequently, butadiene may be plasma-polymerized on the surface of the uncut PTFE film <NUM> using plasma.

Thereafter, as shown in <FIG>, the springs <NUM> are gradually pressed downward by the first parting surface <NUM> of the first block <NUM>, whereby the second lower parting surface <NUM> of the second block <NUM> is gradually moved closer to the vicinity of the third parting surface <NUM> of the third block <NUM>. Accordingly, the cutting portions <NUM>, provided on the second lower parting surface <NUM>, are pressed in contact with the uncut PTFE film <NUM> with a predetermined strength by the reaction forces of the springs <NUM>. It should be noted that in this phase, the uncut PTFE film <NUM> has not been completely cut yet by the cutting portions <NUM> provided on the second lower parting surface <NUM>. Instead of the springs <NUM>, for instance, one or more hydraulic cylinders or so forth may be configured to act on the second block <NUM> such that the second lower parting surface <NUM> is gradually moved closer to the vicinity of the third parting surface <NUM>, whereby the cutting portions <NUM> are pressed in contact with the uncut PTFE film <NUM> with a predetermined strength.

Subsequently, as shown in <FIG>, the first parting surface <NUM> of the first block <NUM> is contacted to the second upper parting surface <NUM> of the second block <NUM>, and each unmolded gasket body <NUM> is pressed toward each molding recess <NUM> located thereunder in <FIG> at a high pressure (of e.g., <NUM> to several hundred kPa) by each pair of the piston <NUM> and the male threaded screw <NUM> of the first block <NUM>. Accordingly, during molding from each molding elastomer block <NUM> to each gasket body <NUM>, a portion of each molding elastomer block <NUM>, corresponding to the solution contact portion <NUM> of each gasket body <NUM>, presses the uncut PTFE film <NUM> against each molding recess <NUM> at a high pressure. Then, under the pressure, the second lower parting surface <NUM> of the second block <NUM> is further moved closer to the third parting surface <NUM> of the third block <NUM>, whereby the uncut PTFE film <NUM> is cut along the lateral edge of the solution contact portion <NUM> of each unmolded gasket body <NUM> by each cutting portion <NUM> provided on the second lower parting surface <NUM>.

Thus, each unmolded gasket body <NUM> during molding and the uncut PTFE film <NUM> are pressed against each molding recess <NUM> at the high pressure, and simultaneously, the uncut PTFE film <NUM> is cut along the lateral edge of the solution contact portions <NUM> of each unmolded gasket body <NUM>. Because of this, as shown in <FIG>, the circumferential end portion <NUM> of the cut PTFE film <NUM> is stretched, while being sandwiched between the force (material fluid pressure) of each unmolded gasket body <NUM> (each molding elastomer block <NUM>) attempting to expand along each molding recess <NUM> by the elasticity thereof and the reaction force from the lateral surface of each molding recess <NUM>. Simultaneously, the circumferential end portion <NUM> of the cut PTFE film <NUM> is curved toward the slide contact portion <NUM> of each unmolded gasket body <NUM>, while covering the circumferential edge of the solution contact surface <NUM> of each unmolded gasket body <NUM>. Furthermore, the circumferential end surface <NUM> (cut surface) of the cut PTFE film <NUM> is buried in the slide contact portion <NUM> of each unmolded gasket body <NUM> so as not to be exposed to the outside and is made sealed by each unmolded gasket body <NUM>.

Besides, according to the method of manufacturing the gasket <NUM> of the present preferred embodiment, joining of each unmolded gasket body <NUM> and the uncut PTFE film <NUM> and cutting of the uncut PTFE film <NUM> can be completed in a single processing step.

Furthermore, in comparison between pre and post manufacturing states of each gasket <NUM>, an extension ratio Z of the circumferential end portion of the cut PTFE film <NUM> attached to the solution contact surface <NUM> of each gasket body <NUM> is less than or equal to <NUM>%. In more detail, it is preferred to set the extension ratio Z to be less than or equal to <NUM>%. Throughout the specification of the present application, the term "extension ratio Z" refers to a value calculated based on a ratio of an area X to an area Y, where the area X is defined as the area of the solution contact surface <NUM>, to which the cut PTFE film <NUM> is attached, in each gasket body <NUM> (i.e., the area of the cut PTFE film <NUM> stretched in the manufacturing process of each gasket <NUM>), whereas the area Y is defined as the area of a part of the uncut PTFE film <NUM> not attached yet, as the cut PTFE film <NUM>, to each gasket body <NUM>. The extension ratio Z can be expressed by the following formula: (<NUM> - (X/Y)) × <NUM> = Z.

Finally, each gasket body <NUM> and the cut PTFE film <NUM> are taken out from each molding recess <NUM> in the mold <NUM>, whereby manufacturing each gasket <NUM> is completed.

Here, a large number of closed cells, existing inside and on the surface of the cut PTFE film <NUM>, are less likely to be connected to each other in alignment and become the communicating holes than in the prior arts, because the circumferential end portion <NUM> of the cut PTFE film <NUM> is set to have a low extension ratio (of less than or equal to <NUM>%). Besides, the closed cells existing in the circumferential end portion <NUM> are collapsed between the gasket body <NUM> and each molding recess <NUM> at a high pressure in the manufacturing process of the gasket <NUM>. Because of the above, the medical solution <NUM> becomes unlikely to enter the closed cells, whereby it is possible to reduce as much as possible the probabilities that the medical solution <NUM> penetrates the closed cells and leaks out.

The shape and the manufacturing procedure of the gasket <NUM> may be configured as follows instead of those according to the preferred embodiment described above.

The gasket body <NUM> and the cut PTFE film <NUM>, composing the gasket <NUM> according to a modification <NUM>, are shaped as shown in <FIG>. The gasket body <NUM> has an approximately columnar shape and is provided with plural protrusive cross-sectional slide contact portions <NUM> on the lateral surface thereof. Each protrusive cross-sectional slide contact portion <NUM> has an approximately semicircular cross section. It should be noted that each protrusive cross-sectional slide contact portion <NUM> is not limited to have the approximately semicircular cross section. Additionally or alternatively, the number of the protrusive cross-sectional slide contact portions <NUM> is not required to be plural; among the slide contact portions <NUM>, only the one continuing immediately next to the solution contact portion <NUM> may be provided.

Among the slide contact portions <NUM>, the closest one to the solution contact portion <NUM> is formed in continuation to the solution contact portion <NUM>. Obviously, apexes of the slide contact portions <NUM> are each set to have a diameter slightly greater than a diameter (inner diameter) of the inner surface <NUM> of the syringe barrel <NUM> into which the gasket <NUM> is fitted. Besides, small diameter portions <NUM> are formed between the slide contact portions <NUM> adjacent to each other. Each small diameter portion <NUM> has a smaller diameter than each slide contact portion <NUM>. When the gasket body <NUM> is seen in a cross-sectional view, each small diameter portion <NUM> has an approximately straight shape.

As similarly configured in the preferred embodiment described above, the cut PTFE film <NUM> is arranged and set to cover the solution contact surface <NUM> of the solution contact portion <NUM> of the gasket body <NUM>. Besides, the circumferential end portion <NUM> of the cut PTFE film <NUM> extends across the apex of the slide contact portion <NUM> continuing immediately next to the solution contact portion <NUM> (toward the opposite side of the solution contact portion <NUM> from this slide contact portion <NUM>) and is located on a boundary <NUM> between this slide contact portion <NUM> and the small diameter portion <NUM> continuing thereto. Accordingly, the circumferential end surface <NUM> of the cut PTFE film <NUM> is configured to face in surface contact with the lateral surface of the gasket body <NUM> (more specifically, a surface located in a position where the above-mentioned slide contact portion <NUM> ends and the small diameter portion <NUM> begins) on the boundary <NUM>.

Based on the above, as similarly configured in the gasket <NUM> according to the preferred embodiment described above, the circumferential end surface <NUM> of the cut PTFE film <NUM> is not exposed to the outside. Hence, it is possible to prevent occurrence of the undesirable situation that when penetrating the cut PTFE film <NUM>, the medical solution <NUM> leaks out from the circumferential end surface <NUM> through the communicating holes and this brings about leakage of the medical solution <NUM> from the gasket <NUM>.

Next, the manufacturing procedure of the gasket <NUM> according to the modification <NUM> will be explained. The manufacturing procedure is basically the same as that in the preferred embodiment described above. Hence, the manufacturing procedure of the gasket <NUM> will be explained only when the contents thereof are different from those in the preferred embodiment described above; regarding the other contents, the explanation in the preferred embodiment will be incorporated herein by reference.

As shown in <FIG>, the second block body <NUM> of the second block <NUM> includes the molding elastomer block fitting holes <NUM>, each of which is provided with plural slide contact portion molding recesses <NUM> on the inner peripheral surface thereof. The slide contact portion molding recesses <NUM> correspond to the slide contact portions <NUM> except for the one continuing immediately next to the solution contact portion <NUM> of the gasket body <NUM>.

Besides, the third block body <NUM> of the third block <NUM> is provided with the molding recesses <NUM> on the third parting surface <NUM> thereof joined to the second lower parting surface <NUM> of the second block <NUM>. Each molding recess <NUM> corresponds to the solution contact portion <NUM> (the solution contact surface <NUM>) and the slide contact portion <NUM> continuing immediately next to the solution contact portion <NUM> in the gasket body <NUM>.

Then, each gasket body <NUM> during molding and the uncut PTFE film <NUM> are pressed against each molding recess <NUM> at a high pressure, and simultaneously, the uncut PTFE film <NUM> is cut on the boundary <NUM> between the slide contact portion <NUM> continuing immediately next to the solution contact portion <NUM> and the small diameter portion <NUM> continuing to this slide contact portion <NUM> in each gasket body <NUM>. Accordingly, as shown in <FIG>, the circumferential end portion <NUM> of the cut PTFE film <NUM> is stretched, while being sandwiched between the force of each gasket body <NUM> attempting to expand along each molding recess <NUM> by the elasticity thereof and the reaction force from the surface of each molding recess <NUM>. Simultaneously, the circumferential end portion <NUM> is curved to the boundary <NUM>, while covering the solution contact surface <NUM> and the slide contact portion <NUM> continuing immediately next to the solution contact portion <NUM> in each gasket body <NUM>. Furthermore, the circumferential end surface <NUM> (cut surface) of the cut PTFE film <NUM> faces in surface contact with the lateral surface of each gasket body <NUM> (more specifically, a surface located in a position where the above-mentioned slide contact portion <NUM> ends and the above-mentioned small diameter portion <NUM> begins) on the boundary <NUM> so as not to be exposed to the outside.

Claim 1:
A gasket (<NUM>) comprising:
a gasket body (<NUM>) including a solution contact portion (<NUM>) and a slide contact portion (<NUM>) continuing to the solution contact portion (<NUM>), the slide contact portion (<NUM>) having a protrusive cross section; and
a polytetrafluoroethylene (PTFE) film (<NUM>) attached to a solution contact surface (<NUM>) of the solution contact portion (<NUM>) of the gasket body (<NUM>),
wherein a circumferential end portion (<NUM>) of the PTFE film (<NUM>) is curved from the solution contact portion (<NUM>) of the gasket body (<NUM>) so as to extend across an apex of the slide contact portion (<NUM>) immediately next to the solution contact portion (<NUM>), while a circumferential end surface (<NUM>) of the PTFE film (<NUM>) faces in surface contact with a lateral surface of the gasket body (<NUM>) on a boundary (<NUM>) between the slide contact portion (<NUM>) and a small diameter portion (<NUM>) adjacent thereto.