METAL CONTAINER AND METHOD OF MANUFACTURING THE SAME

Abstract: A metal container (10) and a method of manufacturing the same as disclosed herein are provided by attaching a body (11) formed integrally with a top cover (12) to a bottom plate (13) formed separately. The body (11) and bottom plate (13) are sealingly attached together with an adhesive and by a tight curl (16). The tight curl (16) is formed toward the interior of the container (10) and not exposed outside, which makes it very pleasing to the eye.

Description: The present invention relates to a metal container and a method of manufacturing the same. A previously proposed container known as a three-piece can comprises a bottom, a cover and a body and has been widely used for preservation of foodstuffs. The three-piece can is constructed by bending a flat sheet into a cylindrical shape with the seam adhered or welded together to make the body and then curling the bottom and the cover tightly to fasten them to the body. It has also been proposed to form a metal container by drawing and ironing a thin sheet material into a cup-shaped can having a body integral with the bottom and then curling a cover tightly to fasten it to the can. This can is called a two-piece can because of the number of components and is also called a DI can from the drawing and ironing process. Since it is possible to iron the body wall thinly and make the container lightweight, the DI can is economic with regard to consumption of material. The DI can is simple to manufacture and has a good productivity so that it can be mass-produced to meet a great demand. Further, the DI can suffers little leakage and has a good appearance. Consequently, the DI can has rapidly come into wide use as a container for carbonated drinks and beverages having a high internal pressure such as beer and soda, or as an aerosol container for cosmetics. In contrast to the three-piece can which has an exposed seam on the cylindrical body, the two-piece can is advantageous in that it is seamless and has a good display effect, making it suitable for a container for cosmetics which is required to have an attractive appearance. Since the previously proposed DI can is of a construction in which the body is integral with the bottom and the cover is curled tightly to fasten it to the body, the tight curl of the cover is exposed at the shoulder of the container, and detracts from the appearance. Accordingly, there has been proposed a reversed DI can wherein the body is integral with the cover and the bottom is fitted in the body and curled tightly to fasten it to the body. In such a can construction having the cover and the body integral with each other, no curl is formed at the shoulder of the container so that a metal container having a better appearance than the conventional DI can be obtained. However, such a container exposes a curl for fastening the body to the bottom closing the container bottom, and therefore it still remains unpleasing to the eye. FR-A-2220742, which corresponds to the preambles of claims 1 and 15, discloses a metal container for a fluid or gas under pressure, in which a drawn metal body with integral top cover has a metal bottom plate with a central curved surface portion projecting towards the interior of the container. The bottom plate has a cylindrical portion extending parallel to the body and secured thereto by a tightly inwardly curled portion of the body and an adhesive. A first object of the present invention is to provide a metal container and a method of manufacturing the same which appears to have a mono-block construction formed of one-piece member, without exposing an outside tight curl for fastening the bottom to the body. A second object of the present invention is to provide such a container and method of manufacturing the same which has a good seal at the joint between the bottom plate and the body. A third object of the present invention is to provide such a container and method of manufacturing the same which heightens the pressure-resisting strength at the bottom by improving the structure of the bottom plate. A fourth object of the present invention is to provide such a container which prevents occurrence of accidental explosion when the container is heated in a sealed condition by mistake, by using a synthetic resin material for the bottom plate. Other objects and advantages of the present invention will be apparent from the following description. In accordance with a first aspect of the present invention, there is provided a metal container comprising: a metal body having an integral top cover and being formed by drawing and ironing; a metal bottom plate having a central curved surface portion projecting towards the interior of the container and a cylindrical portion extending parallel to said body; an adhesive for attaching said cylindrical portion of the bottom plate to said body; a tight curl formed by tightly curling a lower portion of the body inwardly to fasten it to the cylindrical portion of the bottom plate; and extraction means applied to the top cover for extracting the contents from the container; said bottom plate being fitted in the bottom of said body and attached thereto by said adhesive, and said tight curl fastening said bottom plate to said body so as not to expose said tight curl on the outside of the container; characterised in that a bending portion is formed at the boundary between the curved surface portion and the cylindrical portion, said bending portion has a reduced thickness as compared with the curved surface portion and the cylindrical portion, and said bending portion is arranged to expand in diameter when an internal pressure is applied to the central curved surface portion of the bottom plate. The bottom plate may further comprise an inclined portion extending straight in section between the curved surface portion and the cylindrical portion for providing proper allowance of contraction at the time of fastening tight said body and said bottom plate by curling. The lower end of said bottom plate may be integrally curled in and held tight by said tight curl, or the lower end of the cylindrical portion of the bottom plate may be in contact with the inner surface of said tight curl without being curled therein. Alternatively, the lower end of said bottom plate may be partially held tightly by said tight curl. The adhesive for attaching said body to said bottom plate may be an adhesive applied on the inner surface of said body and/or the outer surface of said bottom plate. The adhesive may comprise a thermoplastic synthetic resin layer coated on the inner surface of said body. Said extraction means applied to the top cover may comprise a spray nozzle mounted thereon. The top cover may further include a bead for mounting the spray nozzle formed by curling a cylindrical opening in the top cover, a spray nozzle mount being attached to said bead to mount said spray nozzle to the top cover. Alternatively, the extraction means may comprise an opening to be formed by removing a portion of the top cover therefrom. With such an arrangement, the metal container may further comprise a tab adapted to be pushed by finger and formed by an upwardly protruding portion of the top cover, said tab including a thin, tear-open portion therearound, whereby said tab is pressed by finger to cut it off from said tear-open portion and form the opening. As a further alternative, the extraction means may comprise a cap detachable by threaded means. In this further alternative arrangement, the top cover may have an upward cylindrical opening and a threaded portion may be formed on the outer circumferential surface thereof so as to make the cap detachable. A synthetic resin threaded tube, having a thread formed on its outer circumferential surface, may be fitted to the cylindrical opening so as to make the cap detachable. In accordance with a second aspect of the present invention there is provided a method of manufacturing a metal container comprising the steps of: (a) blanking and drawing a metal sheet material into a cup; (b) drawing and ironing said cup into a can having a body integral with a top cover, wherein the drawing reduces the diameter of the cup and the ironing elongates the cup and reduces the wall of the body to a predetermined thickness; (c) forming a bottom plate having a central curved surface portion and a peripheral cylindrical portion; (d) applying adhesive means to the body and/or said cylindrical portion; (e) fitting said bottom plate in the bottom of the body so that the central curved surface portion projects inwardly of the body and the cylindrical portion extends parallel to said body; (f) curling tight the lower part of said body inwardly so as to fasten and attach said bottom plate to said body; and (g) forming a closable opening on the top cover; characterised in that the forming step also produces a bending portion which is disposed at the boundary between the curved surface portion and the cylindrical portion and which is of reduced thickness as compared with the curved surface portion and the cylindrical portion. The method may further comprise the step of forming an upward directed cylindrical opening in the centre of the top cover, following the step of drawing and ironing the cup into the can. The method may also comprise the step of forming a bead for mounting a spray nozzle thereto by curling the cylindrical portion. Alternatively, the method may comprise the steps of forming a mouth by cutting the upper end of the cylindrical opening and forming a thread thereon for screwing a cap onto the outer circumference of the cylindrical portion. The method may alternatively comprise the steps of forming an upward tab in the centre of the top cover and forming a thin tear-open portion around said tab. The method may also comprise the step of applying an inner coating on the inner surface of the drawn and ironed can, and may also comprise the step of coating and printing the outer surface of the drawn and ironed can. In the accompanying drawings:- Fig 1 shows stages in the manufacture of a metal container; Fig 2 is a vertical sectional view of a die for curling the body and bottom plate of a metal container of the present invention; Fig 3 is a partially cut-away elevation of an embodiment of metal container according to the present invention; Fig 4 is a sectional view on a larger scale of part of a bottom plate used in the container of Fig 3. Fig 5 is a sectional view on a larger scale showing the fitting of the bottom plate in the container of Fig 3; and Fig 6 is a sectional view through part of the container of Fig 3 showing, in exaggerated form, the body deformation under the internal pressure applied on the bottom plate; A general method of manufacturing a metal container will be described with reference to Fig. 1. A metal sheet 20 such as aluminium, stainless steel, etc., is blanked and drawn into a cup 21 by a cupping press. Then the cup 21 is fed to a process 22 performed by a drawing and ironing press (DI press) where it is redrawn to reduce its diameter, and thereafter undergoes an ironing process 23 with an ironing die so as to elongate the cup and obtain the body wall of a desired thickness. The DI pressed can 24a is fed to a trimmer belonging to the DI press where a lower end portion 25 is trimmed to a certain dimension. The trimmed can is fed to a process 26 for forming a bead at the mouth to which a spray nozzle is mounted. In the bead forming process 26, pressing is performed to form a top cover 12 into a frusto-conical shape and then to form a cylindrical opening 27 protruding upwards in the centre of the top cover. The cylindrical opening 27 corresponds in diameter to a spray nozzle mount. Subsequently, an upper end portion 28 of the cylindrical opening 27 is cut off, followed by a step of forming a bead 29 by curling. The bead formed can 24b proceeds to a washing process, not shown, where its internal and external surfaces are de-greased by alkali shower, etc., water-washed and then dried. The washed can 24b is fed to a inner coating process 29 where its internal surface is coated by spray means 30 and then dried. The inner-coated can 24c is transferred to an outer-coating/printing process 31, where the can is outer-coated and printed by a roller coating means, for example, a coat roller 32 and a shoulder roller 33. The inner-coating process 29 and the outer-coating/printing process 31 may be reversed in order. The thus inner/outer coated and printed can 24d is fed to a bottom plate mounting process 34, where a bottom plate 13 is put in place. In the bottom plate mounting process 34, an adhesive is sprayed on the inner circumferential surface of the lower portion of the can 24d, whereafter the bottom plate 13 is fitted to the can. After the cylindrical portion 16 of the bottom plate 13 and the lower end of the body 11 are sufficiently attached together, the can is inserted in a forming die 35 as shown in Fig. 2 and pressed in the longitudinal direction to tightly curl the cylindrical portion 16 and the body 11 toward the interior of the container and fasten them together. After the tight curling process is finished, the spray nozzle 14 is mounted to the bead 29, whereupon the manufacture of the metal container is completed. The tight curl is not limited to the illustrated type having a circular curl in section. Any sort of inward fold which grips the bottom plate sufficiently firmly to fix it to the body and seal it thereto will suffice. Attachment of the body 11 and the bottom plate 13 is not limited to the spraying of adhesive in a lower portion of the body. The can 24c may be inner-coated with thermoplastic synthetic resin and after the bottom plate 13 is fitted in this can, the inner-coating layer may be melted by electromagnetic induction heating or laser beam so as to join the can and bottom plate 13 together. Melted thermoplastic synthetic resin serves to provide a preliminary seal between the metal sheets of the fitted parts, and the subsequent tight curling process promotes and ensures airtightness at the joint between the body 11 and the bottom plate 13, thereby preventing leakage from the joint even if the container is stored for a long time. The body 11 and the bottom plate 13 are preferably made of the same material. This ensures no difference in thermal expansion therebetween so that no relative slippage occurs at the joint and a reliable sealing structure is attainable. Figs. 3 to 6 show a metal container 110 according to an embodiment of the invention, comprising a body 111 including a top cover 112, and a bottom plate 113, both made of aluminium. The bottom plate 113 has an upward curved portion in the upper centre, as previously mentioned, but in which the periphery, namely the boundary with the cylindrical portion 116, is formed as a thinner bending portion 120. The cylindrical portion 116 has a predetermined external diameter in accordance with the diameter of the body 111 so that it is pressed therein in an interference fit. An adhesive is applied between the cylindrical portion 116 and the body 111. The grade of fit between the body 111 and the bottom plate 113 is determined in accordance with the subsequent right curling process. The lower end of the body 111 protrudes downward from the end of the cylindrical portion 116 by the length corresponding to the cross-sectional length of a tight curl 118. The radius of curvature at the inner circumference of the bending portion 120 is preferably one to three times the thickness of the bottom plate 113. By drawing the bottom plate into such a configuration, the bending portion 120 has approximately 80% thickness of that of the other part. In the embodiment as shown, the body 111 has an internal diameter of 50mm and the bottom plate 113 is 3.8mm thick with the bending portion 120 of about 3.0mm thickness. Further, the radius of curvature at the curved portion of the bottom plate 113 is 50mm which is the same with the internal diameter of the body. Subsequently, the tight curling process is performed by use of a curling die 35 as shown in Fig. 2, whereupon the lower end of the cylindrical portion 116 comes into contact with the inner circumferential lower end of the tight curl 118. When the internal pressure of the pressure container of the above construction increases and the curvature of the bottom plate 113 becomes larger than its initial value, the bending portion 120 thrusts into the body 111 as shown in Fig. 6 and the adhesive seal is promoted by the following action. Namely, when the internal pressure of the pressure container with its bottom closed by the bottom plate 113 increases, the container is under the same condition as if a load were concentrated on the centre portion of the bottom plate 113, and said centre portion tries to deform in reverse and protrude downwardly. At this time, the bottom plate 113 having a partially thin bending portion 120 at the periphery has a weak rigidity in the direction of preventing the reverse deformation so that the peripheral diameter of the bottom plate 113 tries to expand with the increase in the container internal pressure at the stage prior to the reverse deformation, but this diameter expansion, however, is prevented by the body 111. Further, since the cylindrical portion 116 of the bottom plate 113 is in contact with the tight curl 118 and prevented from its axial movement, the cylindrical portion 116 generates a force pressing toward the body 111, thereby increasing contact pressure where the cylindrical portion 116 is attached to the body 111. The increasing tendency of the contact pressure is most remarkable at the upper end of the cylindrical portion 116, i.e. in the proximity of the bending portion 120. (See Fig. 6). Even if the above bottom-sealed pressure container comprises the body 111 and the bottom plate 113 both made of less rigid aluminium, it will exert a sufficient strength against pressure by the above-described action. Further, the tight curl 118 is formed toward the interior of the container 110, therefore the container has a better appearance than the conventional one with the tight curl 118 exposed as the outside. If the adhesive requires a relatively long time (approximately several minutes) for curing, the bottom plate 113 may be pressed in so that the lower end of the cylindrical portion 116 is aligned with that of the body 111, as shown in Fig. 5. The subsequent tight curling process advances, pushing the bottom plate 113 inwardly, and at the completion of this process, the bottom plate 113 is held at a predetermined position and the lower end of the cylindrical portion 116 comes into contact with the inner circumference of the tight curl 118. Further, the body 111 including the top cover 112 and the bottom plate 113 may be made of a tin plate or surface treated steel sheet.

Claims: A metal container comprising: a metal body (111) having an integral top cover (112) and being formed by drawing and ironing; a metal bottom plate (113) having a central curved surface portion projecting towards the interior of the container and a cylindrical portion (116) extending parallel to said body (111); an adhesive for attaching said cylindrical portion (116) of the bottom plate (113) to said body (111); a tight curl (118) formed by tightly curling a lower portion of the body (111) inwardly to fasten it to the cylindrical portion (116) of the bottom plate (113); and extraction means applied to the top cover (112) for extracting the contents from the container; said bottom plate (113) being fitted in the bottom of said body (111) and attached thereto by said adhesive, and said tight curl (118) fastening said bottom plate (113) to said body (111) so as not to expose said tight curl (118) on the outside of the container; characterised in that a bending portion (120) is formed at the boundary between the curved surface portion and the cylindrical portion (116), said bending portion (120) has a reduced thickness as compared with the curved surface portion and the cylindrical portion (116), and said bending portion (120) is arranged to expand in diameter when an internal pressure is applied to the central curved surface portion of the bottom plate (113). A container as claimed in claim 1, wherein said bottom plate (113) further comprises an inclined portion extending straight in section between the curved surface portion and the cylindrical portion (16, 116) for providing proper allowance of contraction at the time of fastening tight said body (111) and said bottom plate (113) by curling. A metal container as claimed in claim 1 or 2, wherein the lower end of said bottom plate is integrally curled in and held tight by said tight curl. A metal container as claimed in claim 1 or 2, wherein the lower end of the cylindrical portion of the bottom plate is in contact with the inner surface of said tight curl without being curled therein. A metal container as claimed in claim 1 or 2, wherein the lower end of said bottom plate is partially held tightly by said tight curl. A metal container as claimed in any preceding claim, wherein said adhesive for attaching said body to said bottom plate is an adhesive applied on the inner surface of said body and/or the outer surface of said bottom plate. A metal container as claimed in claim 6, wherein said adhesive comprises a thermoplastic synthetic resin layer coated on the inner surface of said body. A metal container as claimed in any preceding claim, wherein said extraction means applied on the top cover comprises a spray nozzle mounted thereon. A metal container as claimed in claim 8, wherein the top cover further includes a bead for mounting the spray nozzle formed by curling a cylindrical opening in the top cover, a spray nozzle mount being attached to said bead to mount said spray nozzle to the top cover. A metal container as claimed in any one of claims 1 to 7, wherein said extraction means comprises an opening to be formed by removing a portion of the top cover therefrom. A metal container as claimed in claim 10, further comprising a tab adapted to be pushed by finger and formed by an upwardly protruding portion of the top cover, said tab including a thin, tear-open portion therearound, whereby said tab is pressed by finger to cut it off from said tear-open portion and form the opening. A metal container as claimed in any one of claims 1 to 7, wherein said extraction means comprises a cap detachable by threaded means. A metal container as claimed in claim 12, wherein the top cover has an upward cylindrical opening and a threaded portion is formed on the outer circumferential surface thereof so as to make the cap detachable. A metal container as claimed in claim 13, wherein a synthetic resin threaded tube, having a thread formed on its outer circumferential surface, is fitted to the cylindrical opening so as to make the cap detachable. A method of manufacturing a metal container comprising the steps of: (a) blanking and drawing a metal sheet material (20) into a cup (21); (b) drawing and ironing said cup (21) into a can (24a) having a body integral with a top cover (12), wherein the drawing reduces the diameter of the cup (21) and the ironing elongates the cup (21) and reduces the wall of the body (11, 111) to a predetermined thickness; (c) forming a bottom plate (13, 113) having a central curved surface portion and a peripheral cylindrical portion (16, 116); (d) applying adhesive means to the body (11, 111) and/or said cylindrical portion (116); (e) fitting said bottom plate (13, 113) in the bottom of the body (11, 111) so that the central curved surface portion projects inwardly of the body and the cylindrical portion (16, 116) extends parallel to said body (11, 111); (f) curling tight the lower part of said body (11, 111) inwardly so as to fasten and attach said bottom plate (13, 113) to said body;and (g) forming a closable opening on the top cover; characterised in that the forming step (c) also produces a bending portion (120) which is disposed at the boundary between the curved surface portion and the cylindrical portion (16, 116) and which is of reduced thickness as compared with the curved surface portion and the cylindrical portion. A method of manufacturing a metal container as claimed in claim 15, further comprising the step of forming an upward directed cylindrical opening in the centre of the top cover, following the step of drawing and ironing the cup into the can. A method of manufacturing a metal container as claimed in claim 16, further comprising the step of forming a bead for mounting a spray nozzle thereto by curling the cylindrical portion. A method of manufacturing a metal container as claimed in claim 16, further comprising the steps of forming a mouth by cutting the upper end of the cylindrical opening and forming a thread thereon for screwing a cap onto the outer circumference of the cylindrical portion. A method of manufacturing a metal container as claimed in claim 15, further comprising the steps of forming an upward tab in the centre of the top cover and forming a thin tear-open portion around said tab. A method of manufacturing a metal container as claimed in any of claims 15 to 19, further comprising the step of applying an inner coating on the inner surface of the drawn and ironed can. A method of manufacturing a metal container as claimed in any of claims 15 to 20, further comprising the step of coating and printing the outer surface of the drawn and ironed can.

Inventors: HAMAGUCHI, MASAMI, HIRAOKA, OSAMU, TAKAHASHI, OSAMU, YANAGIHARA, HIROMU
Applicants: ASIA CAN COMPANY LIMITED, SHISEIDO COMPANY LIMITED
Application year: 1987
Main classification: B65D83
IPC codes: B65D83