PRODUCTION METHOD FOR RUBBER PLUG FOR VIAL

Abstract: This invention relates to a production method for a rubber plug for a vial characterized in that a synthetic resin film is laminated on the leg side of a rubber plug. The production method comprises (i) a first formation step of superposing a synthetic resin film (1) resistant to medicines or to medical chemicals onto an unvulcanized rubber sheet (2) and pressing, heating and shaping them between moldes (A, B); a second formation step of putting an unvulcanized rubber sheet having substantially the same hole (10) as the root portion of the leg portion (4) of the resulting primary mold over the primary mold from its leg side and pressing, heating and shaping them by a pair of molds; and a step of cutting and removing fins around the resulting secondary mold. The production method of the present invention can mold the rubber plug portion and the synthetic resin laminate portion in one process. Furthermore, since the above steps can be carried out with the materials kept continuous in the sheet form, the method of the invention is particularly advantageous for the production of a large number of rubber plugs for vials.

Description: The present invention relates to a method for producing a rubber stopper for a vial, and more particularly to a method for producing a rubber stopper for a vessel for medicine, which is covered with a synthetic resin film. Generally, medicine in a vial is badly affected by a stopper which is used for a vessel for medicine, where a vulcanization-accelerator and other compounded ingredients contained in the rubber stopper exude in a liquid medicine in the vial, and ingredients contained in the liquid medicine are adsorbed to the rubber. In order to prevent the rubber from affecting the liquid medicine in the vial, a rubber stopper of which surface being contacted with a liquid medicine is laminated with a synthetic resin film having a chemical resistance has conventionally been sometimes used as disclosed in Japanese Examined Patent Publication No. 9119/1979, Japanese Unexamined Patent Publication No. 47637/1982 and so on. Several methods for producing such a covered rubber stopper have been proposed. For instance, as disclosed in the above-mentioned Japanese Examined Patent Publication No. 9119/1979, there is a method wherein a fluorocarbon resin film is formed and cut so as to give a shape corresponding to the shape of a leg portion of a rubber stopper, a mold for forming a rubber stopper is charged with the formed film having a shape corresponding to the shape of the leg portion, moreover a rubber material is poured into the mold, and a rubber stopper is produced by forming and vulcanization. As disclosed in Japanese Examined Patent Publication No. 53184/1982, there is a method wherein a leg portion made of a rubber which is covered with a synthetic resin film is formed and cut, then inserted into the other mold, and the top surface is integratedly formed and bonded with the upper part of the leg portion. However, in these methods, it is necessary that firstly a formed article of a resin film having a shape corresponding to the shape of the leg portion of the rubber stopper is formed or the leg portion made of a rubber which is covered with a film is formed, then cut to pieces one by one, and moreover these pieces are inserted into a mold for forming a final product. The precharacterizing part of claim 1 refers to a method for producing a rubber stopper as disclosed in US-A-4 397 903. The document is directed to an apparatus and a method for producing a rubber stopper having a plug portion and a head portion. The axial end face of the plug portion is provided with a facing or liner made of chemically inert material. The known method broadly consists of laminating a thin sheet of elastomeric material such as uncured rubber, to one face of a thin sheet of inert material being chemically etched to produce a static cling to securely adhere the sheets together. The laminated sheet is cut into a plurality of circular discs of a predetermined size to form the liner facing in the finished article. The discs are then forced into mould cavities for the article to be manufactured. Thereafter, additional elastomeric material is placed into a mould and moulded in a conventional manner. Since the laminated sheet has to be cut into a plurality of circular discs which have to be inserted into a mould, the process for producing a covered rubber stopper is complicated as a whole. It is the object of the present invention to provide a method for producing a covered rubber stopper more efficiently and economically. This problem is solved, according to the invention, with the features of claim 1. As a material of the synthetic resin film resistant to a medicine or a ethical drug, which is used in the method of the present invention, fluorocarbon resin, nylon, polyethylene, polypropylene and the like are given, and these materials are suitably selected in accordance with chemicals which are contained in a vial. It is necessary that these films have an adhesion property to the rubber based upon the vulcanization. As occasion demands, in order to improve the adhesive property, a treatment such as a chemical treatment, a corona discharge treatment or a sputter-etching treatment can be carried out. As a material of the rubber stopper, a synthetic rubber such as butyl rubber, halogenated butyl rubber, butadiene rubber, isoprene rubber, ethylene-propylene rubber or silicone rubber or natural rubber is used. A compounding ingredient for a rubber is usually contained in the material of the rubber. In the method of the present invention, in order to obtain a primary formed article, when the synthetic resin film is piled on an unvulcanized rubber sheet and they are pressed and heated by means of a mold, at the same time the vulcanization is performed, the shape of the rubber stopper which is covered with a film is formed. It is preferable to carry out the pressing and heating in its step so that complete vulcanization can be avoided in consideration of being re-heated in the step for producing a secondary formed article. In the step for producing a secondary formed article, a half-vulcanized rubber sheet finally prevents the synthetic resin sheet from peeling off, and plays a part in sealing or packing when the rubber stopper is used in the vial 13 as shown by a phantom line in Fig. 3. The reason why not an unvulcanized rubber but a half-vulcanized rubber is used in such a rubber sheet is that flowing into the portion of the synthetic resin film is avoided during vulcanization and thereby the surface of the film is prevented from pollution. The degree of vulcanization for the half-vulcanized rubber is suitably decided by the components of the rubber, temperature for vulcanizing in a secondary forming step and the like. Also, the reason for pressing and heating in this step is to obtain a rigid completed secondary formed article by covering and bonding the lower face of the head portion or the whole surface except the plug or leg portion with a rubber layer and completing the vulcanization of the whole rubber. Further, the step for cutting down a flash from a secondary formed article (or for cutting down a completed products from a sheet-like flash) is generally employed in case of manufacturing rubber products from a sheet-like rubber material. Hereinfter, the method of the present invention is concretely explained by examples. The method is described with reference to the accompanying drawings, in which Fig. 1a is a sectional view showing an embodiment of the primary forming step in the method of the present invention; Fig. 1b is a sectional view showing the primary formed article obtained in the primary forming step of Fig. 1a; Fig. 2a is a sectional view showing an embodiment of the secondary forming step in the method of the present invention; and Fig. 2b is a sectional view showing a secondary formed article obtained in the secondary forming step; and Fig. 3, Fig. 4 and Fig. 5 are longitudinal sectional views showing embodiments of a rubber stopper for a vial obtained by the producing method of the present invention. As shown in Fig. 1a, a first mold B which is a lower side mold of a set of molds for the primary forming has a cavity 5 somewhat deeper than a real size of the leg portion (4 in Fig. 3) of the final product, and an upper side second mold A has a cavity 7 which is somewhat shallower than a real size of the head portion (6 in Fig. 3) of the final product Each cavity 5, 7 is provided with a projection 5a, 7a corresponding to the respective recess (4a, 6a in Fig. 1b) to be formed at the center of a product in order to improve forming accuracy. A laminate of a synthetic resin film 1 and an unvulcanized rubber sheet 2 is put between the molds A and B, and forming, vulcanizing and adhesion by crosslinking are carried out by pressing and heating. By the above-mentioned steps, primary formed articles 8 which are still linked with each other through a sheet-like flash which is formed by melting the periphery part of a product once and then re-forming it. The primary formed article has a body of the rubber stopper covered with a synthetic resin material at the lower side (at the leg side) thereof. Though conditions of pressing and heating during the primary forming step are changed in accordance with the kind of the used synthetic resin film and rubber, the kind of compounding ingredients, thickness thereof, size of molds and the like, the conditions are usually 130° to 180°C, 50 to 300 kg/cm² and 5 to 15 minutes. However, the conditions for vulcanization are adjusted so that the hardness of the primary formed article is lower than the hardness of the final product since vulcanization also proceeds when the primary formed article is re-heated in the secondary forming step. Also, in the primary forming step, the primary formed article can be formed by pre-vulcanizing only an unvulcanized rubber sheet 2 to an extent, then opening the molds, putting a resin film therebetween, and pressing and heating again to continue the vulcanization. Next, as shown in Fig. 2a, the under face of the head portion 6 is covered with a half-vulcanized rubber sheet 3 having holes 10 of which diameter is almost the same as that of the root portion 9 of the leg portion 4, of the rubber stopper, which is separately produced. Then, the material is pressed and heated between the second molds C and D having shapes adapted to the shape of the final product, and subsequently the body and the half-vulcanized rubber sheet are vulcanized to give a secondary formed article having a forms shown in Fig. 2b. As the half-vulcanized rubber sheet 3 used in that step, a sheet of 0.5 to 2 mm in thickness can be employed which is produced by vulcanizing a rubber material composed of the same components as the primary product or a rubber material composed of such components that gives a vulcanizing rate slightly higher than the primary formed article at 130° to 180°C for 0.5 to 5 minutes. Finally, the obtained secondary formed articles 11 are take out from the molds C, D, and the final products are struck off in order to remove a sheet-like flash. Thereby, such products, as shown in Fig. 3 are obtained. In the secondary forming step, each of the secondary formed articles can be formed by abutting the molds C and D each other, and finally cutting and removing a flash around the rubber stopper. In the method of the present invention, by properly changing the shape of a cavity of the mold, rubber stoppers for a vial having various shapes as shown in Fig. 4 and Fig. 5 can be produced. In Figs. 3 to 5, the numerals denote the same portions as in Fig. 1a and Fig. 2a. In the method of the present invention, the process is simple since it is not necessary to put each of the leg-shaped-film products or leg portions laminated with a film into the molds one by one, which has been employed in conventional proposed methods. Also, since both a primary formed article and a half- vulcanized sheet with holes have a sheet-like form, those can be easily treated in the process for manufacturing. For example, when a set of molds with multiple cavities is used, a lot of covered rubber stoppers can be manufactured at a time. Accordingly, the covered rubber stoppers can be efficiently and economically mass- produced. In addition, the producing method of the present invention is indeed effective for mass-production by multiple cavities, but it can be also employed in such a case that the rubber stoppers are produced one by one.

Claims: A method for producing a rubber stopper for a vial (13) having a plug portion (4) depending into the opening of the vial and a head portion (6) overlying the axial end face of the vial, in which method a synthetic resin film (1) resistant to medicines or medical chemicals is piled onto an unvulcanized rubber sheet (2), characterized through a primary moulding step for obtaining a primary moulded article (8) by pressing and heating the synthetic resin film (1) and the unvulcanized rubber sheet (2) by using moulds (A,B) comprising a first mould (B) having a cavity (5) being adapted to the shape of the plug portion (4) of the rubber stopper and a second mould (A) having a cavity (7) being adapted to the shape of the head portion (6) of the rubber stopper, a secondary moulding step for obtaining a secondary moulded article by covering the primary moulded article (8) with a half-vulcanized rubber sheet (3) at the underface of the rubber stopper, said half-vulcanized rubber sheet having a hole (10) of which diameter corresponds to the diameter of the plug portion (4) of the rubber stopper, and pressing and heating it by means of a pair of moulds (C,D) being adapted to the shape of the final product to obtain said secondary formed article of which underface except for the plug portion (4) is covered with a rubber layer, and a cutting process for cutting and removing a flash from the secondary formed article. The method of Claim 1, wherein only the unvulcanized rubber sheet (2) used in the primary moulding process is previously pre-vulcanized, and after that the mould (A,B) is opened and the synthetic resin film (1) is stuck by the mould, and subsequently pressing and vulcanizing are carried out again.

Inventors: AOKI YOSHIHIDE, MATSUZAKI MASARU, AOKI, YOSHIHIDE, MATSUZAKI, MASARU
Applicants: NISSHO KK, NISSHO CORPORATION
Application year: 1990
Main classification: B29C43
IPC codes: A61J1, B29C43, B29L9, B29C70, B29L31, B29K21