Laminated rubber stopper

Abstract: A laminated rubber stopper having a new structure, capable of being produced in a simple process with a reduced production cost and being excellent in tightness, and sealing and sanitary properties, comprises a top part (2) having a flange part (3) and a leg part (4) provided under the top part (2) of the rubber stopper and to be inserted into the mouth of a vial, at least a surface thereof to be contacted with the contents of the vial being laminated with a fluoro resin film, in which the lower surface of the flange part (3) has an annular concavity with a cross section of a circular arc from the periphery of the flange (3) to the neck part (7).

Description: This invention relates to a novel structure of a laminated rubber stopper and more particularly, it is concerned with a laminated rubber stopper used for sealing containers, instruments, etc. for medicaments and medical treatments. For a stopper material for a container, instrument, etc. for medicaments and medical treatments, it is desired to have various properties such as heat resistance, compression resistance, softness, chemical inertness and low permeability of gases or water. In particular, rubbers are excellent in sealing properties and natural rubbers have been used for very many years while synthetic rubbers have often been used more recently, for example, isobutylene-isoprene copolymer rubbers (IIR) having been recommended from a sanitary point of view (see US-A-4 441 621). However, these materials have contamination problems such as that curing agents, compounding agents, etc. contained in the rubbers become dissolved in medicaments held in the containers, the contents of the container are adsorbed on the rubber surface; fine grains are formed from the rubber material during the production process or storage, etc. In order to solve these problems a laminated rubber stopper has been proposed in which a part of the rubber stopper to be contacted with the content of a container, or the whole surface of a leg part of the stopper is laminated with a chemically inert resin such as a fluoro resin. Contamination due to contact of a liquid medicament, etc., with a rubber surface can be prevented by the laminated rubber stopper, but in fact, such a proposal cannot be applied to the preparation of drugs since there arise new problems that the leg part laminated with a fluoro resin, etc. is inferior in sealing in the mouth of a vial, to that having an exposed rubber surface and preparation of a thin laminated layer capable of maintaining the elasticity of rubber is difficult. As shown in Fig. 5, on the other hand, the inventor of the prior art has proposed a laminated rubber stopper capable of preventing contamination by forming a laminated layer 5 of a fluoro resin film on a leg part, while maintaining the tightness or sealing property with the container by retaining an exposed rubber surface on an area from the lower surface of a flange part in the top part of a rubber stopper body to the basic part of a leg part (Japanese Patent Publication No. 64062/1993) and a production process for obtaining this structure (Japanese Patent Publication No. 50386/1993). The above described laminated rubber stopper which the inventor of the prior art has proposed is an excellent rubber stopper capable of realizing the desired effects, but it cannot be said to be suitable for application to a container for a very unstable and expensive medicament, for example, biotechnological preparations, and anticancer drugs, which have been developed lately, since a rubber surface is contacted with the lip part of the container although it is not contacted with a liquid medicament. For the production of such a stopper, a complicated process is required comprising forming in two steps using upper and lower metallic molds, thus increasing the production cost. It is an object of the present invention to provide a laminated rubber stopper with a new structure or shape, whereby the disadvantages of the prior art are overcome. It is another object of the present invention to provide a laminated rubber stopper having a new structure, capable of being produced in a simple process with reduced production cost and being so superior in tightness, and sealing and sanitary effectiveness that the rubber stopper can be used with a storage container for unstable and expensive medicaments sensitive to the outside environment, whilst maintaining quality well for a long period of time. These objects can be attained by a laminated rubber stopper according to claim 1. The accompanying drawings illustrate the principle and merits of the present invention in greater detail. Fig. 1 (A), (B) and (C) are respectively a top view, cross-sectional view and bottom view of one embodiment of a laminated rubber stopper of the present invention. Fig. 2 is a partially enlarged cross-sectional view of Fig. 1(B). Fig. 3 (A), (B) and (C) are respectively a top view, cross-sectional view and bottom view of a laminated rubber stopper of the prior art. Fig. 4 is a cross-sectional view of a laminated rubber stopper inserted into an empty vial. Fig. 5 is a cross-sectional view of a laminated rubber stopper of the prior art wherein the flat lower surface of the flange is not laminated and is retained as an exposed rubber surface and the other lower surface is laminated with a resin film. The inventor has found that a laminated rubber stopper having sealing ability comparable to that of the prior art laminated rubber stopper having an exposed rubber surface retained in part, described in the foregoing Japanese Patent Publication, can be obtained by devising the shape of the rubber stopper itself, even if the whole lower surface of the rubber stopper, including the lower surface of the flange in the top part and the whole surface of the lower part, is laminated, and has arrived at the present invention. In addition, it is found that the sealing ability is further improved by applying this new shape of the rubber stopper of the present invention to the prior art rubber stopper of such a type that the basic part of the leg part and the lower surface of the flange part are not laminated and retained as an exposed rubber surface. Specifically, the present invention provides (1) a laminated rubber stopper according to claims 1-5. Fig. 1 (B) is a cross-sectional view of one embodiment of the present invention, in which a rubber stopper body 1 comprises a top part 2 having a flange part 3 and a leg part 4 to be inserted into a vial and the whole of the lower surface of the rubber stopper, i.e. the whole surface from the lower surface of the flange 3 to the leg part 4 is laminated with a layer of a fluoro resin film 5. On the lower surface of the flange part 3 for covering the mouth of a vial is formed an annular concavity with a cross-section of an arc 6, which will hereinafter be referred to as "the concavity", from the periphery of the flange 3 to the neck part 7 with the leg part 4, as shown in Fig. 1. When the rubber stopper is inserted into the vial, the peripheral edge of a lip portion of the vial fits the basic part of the leg part in the rubber stopper, i.e. the neck part 7 which is a boundary between the lower surface of the flange and the periphery 8 of the flange 3 as shown in Fig. 1 or Fig. 2 by means of the presence of the concavity 6 and dispersion of the surface precision on the peripheral edge of a lip portion of the vial is absorbed by the presence of the concavity 6 to result in close contact and sealing. In the present invention, furthermore, it is desired that dimension R provided in the cross-section of the neck part 7 at the boundary of the basic part of the leg part and the lower surface of the flange part is rendered smaller than that of the prior art, so as to further improve adaptability to the peripheral edge of a lip portion of the vial and increase the air-tightness. In the laminated rubber stopper of the present invention, at least the surface of the rubber stopper to be contacted with the contents of a vial is laminated with a fluoro resin film and the tightness of the fit with the vial is greatly improved, as described above, so as to increase the storage ability of the contents of the vial by devising the shape of the lower surface of the flange and optionally retaining an area from the basic part of the leg part to the lower surface of the flange as an exposed rubber surface. In the case of wholly laminating the lower surface of the rubber stopper but retaining an exposed rubber surface on only the basic part of the leg part, the advantages of the present invention can similarly be obtained. Even when laminating the whole of the lower surface of the rubber stopper, the sealing ability which has hitherto not been attained by the prior art rubber stopper whose lower surface is wholly laminated can be obtained according to the present invention, and since all the parts of the rubber stopper in contact with the vial, from the peripheral edge of the lip portion of the vial to the inner wall at the mouth of the vial, and all the parts of the rubber stopper in contact with a medicament liquid, etc., contained in the vial, are completely laminated in the present invention, there is no fear of contamination due to an exposed rubber surface. Provision of a lamination on the upper surface side of the rubber stopper is of course optionally included in the stopper of the present invention. Production of the laminated rubber stopper can generally be carried out by using a metallic mold for forming the lower surface of the top part, in which a concavity corresponding to the above described cross-sectional shape is formed, in the process described in, for example, Japanese Patent Publication No. 50386/1993, thus obtaining a laminated rubber stopper having exposed rubber surfaces retained on the base part of the leg part and lower surface of the flange. On the other hand, a rubber stopper of the present invention, having laminated layers continuously from the lower surface of the flange to the whole surface of the leg part, can generally be produced by using a lower metallic mold for forming a lower surface of a top part (lower surface of the flange) and a leg part, in which R corresponding to the above described cross-sectional shape is formed previously, arranging a rubber raw material laminated with a fluoro resin film on the lower metallic mold, arranging, on the other hand, a non-laminated rubber material or laminated rubber material on an upper metallic mold corresponding to the shape of the upper surface of the top part and subjecting the resulting assembly of the upper and lower metallic molds to compressing and molding in one stage. In the laminated rubber stopper of the present invention, as the annular concavity having a cross-section of an arc on the lower surface of the flange part, R in the cross-section preferably has a radius of curvature of 0.05 to 0.5 mm, more preferably 0.1 to 0.33 mm, most preferably 0.15 to 0.20 mm. R of the neck part as the boundary of the flange part and leg part has a radius of curvature of preferably smaller than that of 1.5 to 0.5 mm in the prior art, more preferably at most 1/3 of that of the prior art, most preferably a radius of curvature of 0.01 to 0.4 mm. As the rubber material for the laminated rubber stopper of the present invention, there can be used, without limiting to them, for example, isobutylene-isoprene copolymer rubbers (IIR), chlorinated rubbers of IIR, brominated rubbers of IIR, and isobutylene-isoprene-divinylbenzene ternary copolymer rubbers. Examples of the fluoro resin used in the present invention include tetrafluoroethylene resins, trifluorochloroethylene resins, tetrafluoroethylene-hexafluoropropylene copolymer resins, vinylidene fluoride resins, vinyl fluoride resins, tetrafluoroethylene-ethylene copolymer resins (ETFE), and trifluorochloroethylene-ethylene copolymer resins. The thickness of the laminated layer is, for example, 0.01 to 0.2 mm. Production of the laminated rubber stopper of the present invention can be carried out by other processes in addition to the above described process, for example, comprising subjecting to compressing, crosslinking and molding by the use of upper and lower metallic molds having the specified shape according to the present invention, a non-vulcanized rubber sheet to the surface of which fluoro resin fine powder is allowed to adhere or a non-vulcanized rubber sheet which is coated with or immersed in a solution of a fluoro resin, followed by drying. The following examples are given in order to illustrate the invention without limiting it. Example 1 A laminated rubber stopper for a vial according to the present invention was prepared as shown in Fig. 1 (A), (B) and (C) being respectively a top view, cross-sectional view and bottom view of a laminated rubber stopper of the present invention. Referring to Fig. 1, letters a to e show the dimensions of the rubber stopper, i.e. a 19.0 mm, b 13.2 mm, c 8.5 mm, d 3.0 mm and e 5.5 mm. Fig. 2 is a partially enlarged cross-sectional view of Fig. 1B. In this Example, the body of a rubber stopper 1 was formed of IIR, the cross-section of the lower surface of a flange part 3 was moderately curved with a radius of curvature of 3.65 mm and the deepest part of the annular concavity 6 had a depth of 0.3 mm. The radius of curvature the cross-section at a neck part 7, adjacent to the base part of a leg part 4 was 0.1 mm. In Fig. 1, 5 designates a laminated layer consisting of a fluoro resin film (ETFE) with a thickness of 0.05 mm from the periphery of the flange over the whole lower surface of the rubber stopper. A top surface side 2 was also laminated with the same resin film with a concave portion showing an injection needle piercing area. Each of one hundred laminated rubber stoppers of this Example was inserted into a vial with a mouth inner diameter (central value) of 12.3 mm, 12.5 mm and 12.7 mm and subjected to an air-leakage test (vacuum retention test). The results (average value of one hundred samples) are shown in Table 1. Air-leakage test (vacuum retention test) : The zero adjust button of an electronic digital manometer is adjusted to +O Torr. A rubber stopper sample is half-inserted into the mouth of an empty vial so that the leg part is inserted into the vial mouth to such an extent that air in the vial can flow outward and be charged into a vacuum chamber. When the vacuum chamber is evacuated by a vacuum pump and maintained for 3 seconds, the rubber stopper is completely inserted into the vial. The injection needle piercing area of the stopper completely inserted into the vial is pierced by an injection needle (22G) connected with the electronic digital manometer and the degree of vacuum in the vial is measured, during which the degree of vacuum immediately after inserting and after passage of a predetermined time is compared to estimate the retention of vacuum. In this Example, when the difference in degree of vacuum between immediately after inserting and after passage of 24 hours is less than 200 Torr, the retention of vacuum is judged as "good", i.e. no leakage. Comparative Example 1 One hundred samples of laminated rubber stoppers of the prior art were prepared, in each of which the whole surface of the lower side of the rubber stopper was laminated and the lower surface of the flange was flat, as shown in Fig. 3 (A), (B) and (C) being respectively a top view, cross-sectional view and bottom view, and inserted into vials and subjected to an air-leakage test in an analogous manner to Example 1. The results (average value of one hundred samples) are shown in Table 1. In Fig. 3, reference numerals in common with Fig. 1 have the same meanings as Fig. 1, and 3' designates a flange part whose lower surface is concavity-free and plane-shaped. The dimensions a to e are the same as that of Fig. 1. Example 2 One hundred samples of laminated rubber stoppers according to the present invention were prepared in an analogous manner to Example 1 except retaining an exposed rubber surface from the lower surface of the flange part to the periphery of the base of the leg part, in Fig. 1, inserted into vials and subjected to an air-leakage test in an analogous manner to Example 1. The results (average value of one hundred samples) are shown in Table 1. Comparative Example 2 One hundred samples of laminated rubber stoppers, as shown in Fig. 5, were prepared in an analogous manner to Example 2 except retaining an exposed rubber surface from the lower surface of the flange part to the periphery of the base of the leg part, in Fig. 3, inserted into vials and subjected to an air-leakage test in an analogous manner to Example 1. The results (average value of one hundred samples) are shown in Table 1. One hundred samples of each of the laminated rubber stoppers of Examples 1 and 2 and Comparative Examples 1 and 2 were tested according to the Elution Test Method of the Japanese Patent Pharmacopoeia, 12th Revision. Distilled water was charged into a 100 ml vial in such a manner that the leg part of the rubber stopper was brought into contact with the water in a proportion of 2 ml per 1 cm 2 of surface area, the vial was sealed by inserting the rubber stopper sample, fastened by an aluminum cap and heated at 121 °C for 60 minutes in an inverted state in an autoclave. The liquid in the vessel was then used as a test liquid and subjected to the above described extraction test to obtain results as shown in Table 2. From these results, it is apparent that in the items of the extraction test, the laminated rubber stoppers of the present invention show very little elution and excellent sanitary properties. Furthermore, three samples of each of the laminated rubber stoppers of Example 1 and Comparative Example 2 were subjected to measurement of out-gases by gas chromatography. This test was carried out to measure a very small amount of an out-gas extracted into the head space of a vial from the rubber stopper. Specifically, as shown in Fig. 4, a rubber stopper sample was inserted in an empty 10 ml vial, fastened by an aluminum cap, and maintained in a drier at 100 °C for 1 hour. Then, 1000 µl of the gas in the vial was taken and subjected to gas chromatography analysis. Using detected peaks of these samples, the total amounts of the out-gases were obtained from the peak areas (cm 2 ) and compared to obtain results as shown in Table 3, in which a smaller area shows a smaller amount of the out-gas. It can be confirmed from the results of Table 3 that the sample of the present invention can favorably be compared with that of the prior art sample as to the decreased total amount of out-gas and improved sanitary properties. The analysis by chromatography was carried out under the following conditions: Gas chromatography apparatus manufactured by Shimazu Seisakusho Co., Ltd [Shimazu GC-144: FID dual detector -commercial name-], column: BENTONE 34 + DIDP (5 + 5 %), UNIPORT + HP 80/100 -commercial name-, glass column (3 mm⊘ x 3 m), feed part temperature: 105 °C, column temperature: 70 °C, detector temperature: 115 °C, flow rate: H 2 0.5 kg/cm 2 , air 0.5 kg/cm 2 , N 2 42 ml/min, range: 10 2 . Gas Chromatography Test Results (total peak area; cm 2 ) First Time Second Time Third Time Average Value Comparative Example 2 516 475 508 500 Example 1 168 147 178 164 As illustrated above, the laminated rubber stopper of the present invention has the great advantages on a commercial scale that the problem of contamination from a raw rubber material can be solved and air-tightness can be secured by devising the lower surface of the flange part of the stopper and the cross-sectional shape of the neck part, whereby contents such as expensive and unstable medicaments, can be stored without deterioration of quality for a long period of time and production of the stoppers can be carried out in simple manner so as to reduce their cost.

Claims: A laminated rubber stopper comprising a top part (2) having a flange part (3), a leg part (4) and a neck part (7) connecting the flange part to the leg part, the leg part being provided under the top part of the rubber stopper and to be inserted into the mouth of a vial, at least the surface thereof which is to be contacted with the contents of the vial being laminated with a fluoro resin film, characterized in that the lower surface of the flange part is formed with an annular concavity (6) with a cross section of an arc from the periphery of the flange to the neck part. A laminated rubber stopper as claimed in Claim 1, wherein the whole surface of the leg part (4) is laminated except the periphery of the basic part thereof. A laminated rubber stopper as claimed in Claim 1, wherein at least the whole of the lower surface side of the rubber stopper is laminated with a fluoro resin film. A laminated rubber stopper as claimed in any one of Claims 1 to 3, wherein the annular concavity (6) with a cross-section of an arc has a depth of 0.3 mm. A laminated rubber stopper as claimed in any one of Claims 1 to 4, wherein the neck part has a dimension R of 0.01 to 0.4 mm in radius of curvature. A container of a medicament when sealed with a laminated rubber stopper according to any one of claims 1 to 5.

Inventors: SUDO MORIHIRO, SUDO, MORIHIRO
Applicants: DAIKYO SEIKO LTD, DAIKYO SEIKO, LTD.
Application year: 1996
Main classification: B65D39
IPC codes: B65D39, B65D51, A61J1