Patent Publication Number: US-2009223956-A1

Title: Can container

Description:
TECHNICAL FIELD 
     This invention relates to a can container such as an aerosol can to be filled with contents. 
     BACKGROUND ART 
     Aerosol cans filled with a propellant as a high pressure gas are used in the prior art of this kind of aerosol can is thrown into the fire or left in a hot place over a prolonged period of time, an inner pressure of the can container is raised extraordinarily due to thermal expansion of a propellant. In this case, a seamed portion where a can body and a bottom lid are seamed, or an installation portion of the can body where a mountain cap is mounted thereon may be demolished and the bottom lid of the can container or the mountain cap is thereby blown off. In order to prevent such an explosion of the can container resulting from a pressure rise, a weakened portion is formed to release the inner pressure of the can container. The weakened portion is to be ruptured when the inner pressure of the can container exceeds a certain value so that the can container is deformed. Examples of this kind of can containers are disclosed in Japanese Patent Laid-Open No. 47-7686 (corresponding to U.S. Pat. No. 3,786,967) and Japanese Patent Laid-Open No 48-49591 (corresponding to U.S. Pat. No. 4,003,505). 
     Japanese Patent Laid-Open No 477-686 discloses a can container, in which a plurality of scores is formed equiangularly on a top of a seamed portion where a metal upper lid (i.e., a mountain cap) and a metal body portion are seamed. According to this container, when the inner pressure thereof is raised, the upper lid is deformed to inflate before a bottom lid is blown off. As a result, the scores are ruptured to relief the inner pressure. 
     Japanese Patent Laid-Open No 48-49591 discloses a can container comprising a weakened part at its bottom which is enclosed by a plurality of scores so that the resistance thereof is weakened. This weakened part deforms when the inner pressure exceeds a certain level and the scores are thereby ripped. According to this can container the scores are formed on the wall of the bottom portion, and tearing of the scores takes place only when the bottom portion is deformed outwardly (i.e., when the bottom portion of the can container protrudes outwardly). 
     However, in case of the invention disclosed in Japanese Patent Laid-Open No 47-7686, the scores are formed on the seamed portion of the metal can container so that sealing characteristics of the seamed portion is unstable. For this reason, the contents or propellant may leak from the seamed portion in spite of the inner pressure of the can is proper. Moreover, a rupture of the scores may be induced by an impact or vibration in transit and this also results in a leakage of the contents or propellant from the ruptured portion. Further, if the can container is dropped accidentally, the seamed portion may collide directly with the ground and this makes the score lines formed on the seamed portion easy to be ruptured. As a result of this, the contents may be released even when the inner pressure is not high enough to rupture the scores lines. 
     Meanwhile, according to the invention disclosed in Japanese Patent Laid-Open No 48-49591, the scores are formed at the periphery of the curved part of the bottom portion of the can container. Therefore, in case the bottom portion is deformed to protrude outwardly when the inner pressure exceeds a certain level, a center and its vicinity of the bottom portion is displaced toward the outer side of an axial direction of the can container, however, a central domed wall itself is not deformed significantly. For this reason, if the scores are formed at the periphery of the curved portion of the bottom portion but situated comparatively near the center, the scores may not be ruptured even when the bottom portion is deformed to protrude outwardly. 
     DISCLOSURE OF THE INVENTION 
     The present invention has been conceived noting the technical background as thus far described, and its object is to provide a can container comprising an easily rupturable portion, which is certainly ruptured to release a gas in the can in case an inner pressure of the can is raised extraordinary and which is not ruptured in any other case. 
     In order to achieve the above-mentioned object, according to the invention, there is provided a can container, which has an annular ground contacting portion formed at a lower end of the can container and a domed portion protruding inward of the can container from an inner circumferential face of the annular ground contacting portion, characterized in that: an easily rupturable portion, which is ruptured when an inner pressure of the can is raised extraordinary and the domed portion is thereby deformed to protrude outward of the can container, is formed on an outer face side of the domed portion and situated in the close vicinity of an outer circumferential portion of the domed portion continuing into the annular ground contacting portion. 
     According to the invention, the easily rupturable portion may also be formed radially inward of the outer circumference of the domed portion within a predetermined range. 
     According to the invention, the easily rupturable portion may be a score line whose longitudinal section is an inverted trapezoidal shape formed by a pair of inclined lateral faces which are tapered from the face side toward the inner face side of the domed portion and a bottom face connecting end portions of the lateral faces at the inner face side of the domed portion. 
     According to the invention a planar shape of the easily rupturable portion is an approximate semicircular shape, and end portions thereof may be extended approximately in the radial direction of the can container. 
     Therefore, according to the invention, when the inner pressure of the can container is raised extraordinary by heat or the like the domed portion is inflated and deformed to protrude outwardly of the can container, within the outer circumferential portion of the domed portion formed on the bottom side of the can container (i.e. a lower edge of the domed portion continuing into the annular ground contacting portion which is to be contacted directly with the ground when the can container stands upright). As a result the easily rupturable portion is ruptured to release the contents of the can container For this reason a gas venting can be achieved without blowing apart a piece of the can container, when the inner pressure is raised extraordinary. In addition since the easily rupturable portions are formed in the close vicinity of the outer circumferential portion of the domed portion where the degree of deformation resulting from inflation is great the easily rupturable portions can be ruptured certainly when the domed portion is inflated. The easily rupturable portions can be prevent from being ruptured unexpectedly by dropping impact by forming them on the outer face side of the domed portion in the close vicinity of the outer circumferential portion of the domed portion in comparison with the case in which the easily rupturable portions are formed on the annular ground contacting portion which is likely to collide directly with the ground if the can container is dropped accidentally. 
     Also, according to the invention, since the easily rupturable portions are situated radially inward of the outer circumferential portion of the domed portion within a predetermined range, the easily rupturable portions can be ruptured more certainly. 
     Moreover, according to the invention, the cross-sectional shape of the easily rupturable portions is an inverted trapezoidal shape formed by a pair of inclined lateral faces and a bottom face connecting the inclined lateral faces. This means that the a clearance is created between the inclined lateral faces in the amount of the bottom face when the inner pressure is raised to a certain level by heat or shock and the domed portion is thereby inflated little bit outwardly. For this reason, the easily rupturable portion will not be ruptured undesirably. 
     Further, according to the invention, since a planar shape of the easily rupturable portion is an approximate semicircular shape and end portions thereof are extended approximately in the radial direction of the can container, the semicircular portion enclosed by the ruptured easily rupturable portion is easy to pop up outwardly when the domed portion is deformed to protrude outwardly and the easily rapturable portion is thereby ruptured, in comparison with the case in which the easily rapturable portion is formed linearly. For this reason, the pressure in the can container can be relieved promptly. Additionally, since the end portions of the easily rupturable portion are not directed to the adjoining easily rupturable portion in the circumferential direction, the rupture of the easily rupturable portion will not attack to the adjoining easily rupturable portion even if the propagation of the rupture extends beyond the end portion of the easily rupturable portion For this reason, the domed portion will not be fractured partially. 
     In addition to the above, according to the invention, it is preferable to situate at least a portion of the easily rupturable portion within the range of 3 mm form the outer circumferential portion of the domed portion. Also, a width of a bottom face of the score line is preferably 0.03 mm to 0.1 mm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a bottom view showing a can container of the invention. 
         FIG. 2  is a view showing a situation of the easily rupturable portion of the can container illustrated in  FIG. 1 . 
         FIG. 3  is a longitudinal sectional view showing the domed portion of the invention. 
         FIG. 4  is an enlarged view showing the domed portion illustrated in  FIG. 3 . 
         FIG. 5  is an enlarged view of V portion in  FIG. 4 . 
         FIG. 6  is a longitudinal sectional view showing the can container of the invention. 
         FIG. 7  is a front view showing the can container of the invention. 
         FIG. 8  is a bottom view showing another example of the can container of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, embodiments of the present invention will be explained with reference to the accompanying drawings.  FIGS. 6 and 7  respectively shows a metal can container such as an aerosol can which is filled with a propellant as a high pressure gas. The can container (i.e., a main body)  1  comprises a cylindrical metal can body (i.e., a trunk portion)  2 . An (not shown) aerosol valve member is attached to one of the end portion of the can body  2 , and a disc shaped metal bottom lid (or can lid)  3  is fixed to another end portion of the can body  2  by a seaming method. Contents to be filled in the can container  1  can be exemplified by cosmetics, an insecticide, a medical agent, a detergent, coating compositions, a lubricant, foods and so on, and a high pressure gas is also filled therein as a propellant. 
     A main material of the can body and the can lid of the can container according to the invention is a metal material, in which a proper surface treatment or plating is applied according to need after the process of rolling. At least a metal material, in which a resin coating is applied to a surface to be contacted with the contents can be used. As a metal sheet material, steel sheet materials, e.g., a pure aluminum or aluminum alloy sheet, an electrolytic chromate treated steel sheet a nickel-plated steel sheet, a tin plated steel sheet or the like can be used. Meanwhile, as to the resin coating, coating composition as exemplified by an epoxy-phenol resin an epoxy-acrylate resin, a polyvinyl chloride series resin or the like, and a resin film composed of one or more thermoplastic resin(s) as exemplified by a polyethylene, polypropylene, polyester, polyamide, ionomer or the like, can be suitably used in view of corrosion resistance and workability. 
     The can body  2  is formed by forming a seamless can by drawing and ironing a thin metal sheet and a bottomed cylindrical portion  2 A which is diametrically smaller than the can body  2  is formed by drawing the bottom side of the seamless can. Then, an opening end of the can body  2  and the leading end of the bottomed cylindrical portion  2 A are trimmed, and an opening curled portion  2 B to which an aerosol valve member is mounted is formed on the bottomed cylindrical portion  2 A side. Further, a flange portion  2 C which is to be seamed with the bottom lid  3  is formed on the opening end of the can body  2 . On the other hand, the bottom lid  3  is formed by forming a score line L as an easily rupturable portion  5  on the metal sheet material and punched out into a disc shape, and then a press forming is applied thereto. The bottom lid  3  comprises a domed portion  3 A, which protrudes inward of the can container  1  when seamed with the can body  2  and whose longitudinal section is arcuate, and a flange portion  3 B to be fixed with the can body  2  by a seaming method. 
     As illustrated in  FIG. 1 , score lines L, whose planar shape is semicircle are formed on the outer face side of the can container  1  in the vicinity of an outer circumferential portion  3 C continuing into the flange portion  3 B. More specifically four score lines L are formed equiangularly on the radially outermost portion of the domed portion  3 A. Each score lines L functions as the easily rupturable portion  5  which is to be ruptured when the domed portion  3 A is deformed. In  FIGS. 1 and 2 , the score lines L are situated at the radially outermost portion of the bottom lid  3  in the close vicinity of the outer circumferential portion  3 C of the domed portion  3 A within a range of 3 mm from the outer circumferential portion  3 C, and both end portions of the score line L are directed radially inward of the bottom lid  3 . Here, a two-dot chain line M in  FIG. 2  represents a state where the score line L contacts with the outer circumferential portion  3 C of the domed portion  3 A. 
     A shape of a longitudinal section of the score line L shown in  FIGS. 4 to 5  is an inverted trapezoidal shape formed by a pair of inclined lateral faces  5 A which are tapered from the outer face side of the bottom lid  3  (or the can container  1 ) toward the inner face side thereof and a bottom face  5 B connecting lower end portions of the lateral faces  5 A substantially in parallel with the bottom lid  3 . According to this embodiment, a thickness of the domed portion  3 A of the bottom lid  3  is 0.3 mm, a residual thickness underneath the score line L is 0.15 mm, a width of the bottom face  5 B is 0.06 mm, and an opening degree of the pair of inclined lateral faces  5 A is 50-degree. Additionally a pressure capacity of the bottom lid  3  is degraded if the score lines L are formed too many. For this reason it is preferable to for 2 to 10 score lines L in the circumferential direction of the bottom lid  3  at approximately even interval, within the above-mentioned values. 
     The can container of the present invention shown in  FIG. 6  is formed by attaching the bottom lid  3  to the can body  2  by a seaming method, and a seamed portion  3 D, where the can body  2  (or the flange portion  2 C) and the bottom lid  3  (or the flange portion  3 B) are seamed together, corresponds to the annular ground contacting portion of the present invention. The seamed portion  3 D comprises an annular ground contacting face which is to be contacted with a floor or a table directly and inner and outer circumferential faces  3 E and  3 F extending from a circumferential portion of the ground contacting face near-vertically. An upper end of an inner circumferential wall of the seamed portion  3 D and the outer circumferential portion  3 C (i.e., a lower end of the domed portion  3 A) are connected with each other. 
     As an another embodiment of the present invention shown in  FIG. 8 , an auxiliary score lines  6  pay also be formed radially inward of each score line L situated in the close vicinity of the outer circumferential portion  3 C of the domed portion  3 A. A residual thickness under the auxiliary score line  6  is thicker than that under the score line L. In this case, a stress concentration at the score line L as forming the score lines can be relaxed by forming the auxiliary score line  6  in addition to the score line L. For this reason, the score line L is prevented from being thinned partially too much and from suffering a crack. If the score line is damaged when it is formed, such damage may get more serious as a result of forming the domed portion  3 A, especially in case of forming the domed portion  3 A after forming the score line. 
     Consequently, the resin film covering the inner face of the score line may tear and the score line itself may crack. However, it is possible to avoid such disadvantages by forming the auxiliary score line  6 . 
     According to the can container of the present invention, when the inner pressure of the can container  1  is raised extraordinary by heat or the like, the domed portion  3 A is inflated and deformed to protrude outwardly of the can container  1 , within the outer circumferential portion  3 C around the domed portion  3 A of the bottom lid  3 . At the moment, any of the score lines L formed in the close vicinity of the outer circumferential portion  3 C of the domed portion  3 A is ruptured to release the (not shown) contents inside of the can container  1 . For this reason, the seamed portion  3 D where the can body  2  and the bottom lid  3  are seamed will not be demolished so that the bottom lid  3  will not be blown off. 
     When the domed portion  3 A is deformed to protrude outwardly the center portion of the domed portion  3 A is displaced outwardly (i.e., downwardly) in the axial direction of the can container  1  but the wall surface of the domed portion  3 A itself is not deformed significantly. However, the wall surface in the close vicinity of the outer circumferential portion  3 C of the domed portion  3 A is deformed significantly, more specifically, it is elongated inwardly in the radial direction of the domed portion  3 A and outwardly in the axial direction of the can container  1 . According to the prior art inventions, the score line L is not ruptured when the domed portion  3 A is deformed to protrude outwardly even if the score lines L are formed in the vicinity of the center portion of the domed portion  3 A. On the other hand, according to the present invention, score lines L are formed in the close vicinity of the outer circumferential portion  3 C of the domed portion  3 A. For this reason, it is possible to rupture any of the score lines L certainly when the domed portion  3 A is deformed to protrude outwardly. It is to be especially noted that it is preferable to situate at least a portion of the score lines L within the range of 3 mm from the outer circumferential portion  3 C of the domed portion  3 A inwardly in the radial direction. 
     Therefore, it is possible to rupture the score line L certainly by forming the score lines L within the above-mentioned range. Moreover, the score lines L are formed in the close vicinity of the outer circumferential portion  3 C of the domed portion  3 A, therefore the score line L can be prevented from being ruptured unexpectedly by a drop impact even when the can is dropped accidentally, in comparison with the case in which the score lines are formed on the seamed portion  3 D as the annular ground contacting portion which is to be contacted directly with the ground. Further, according to this embodiment, the longitudinal sectional shape of the score line L is an inverted trapezoidal shape, and the bottom face  5 B is formed to connect the inclined lateral faces  5 A. Therefore, the score line L will not be ruptured undesirably even if the inner pressure of the can container  1  is raised to a certain level by heat or impact to inflate the domed portion  3 A slightly outward. 
     Additionally, the bottom face  5 B cracks when the bottom lid  3  is deformed to protrude outwardly by a rise in the inner pressure of the can container  1  so that the inclined lateral faces  5 A are brought into contact with each other. That is, provided that the lower end portions of the inclined lateral faces  5 A of the score line L are contacted directly with each other without interposing the bottom face  5 B therebetween for example, the inclined lateral faces  5 A may be brought into contact with each other to rupture the score line L even if the inner pressure of the can container is not high enough to deform the bottom lid  3  to protrude outwardly but the domed portion  3 A is slightly inflated outwardly. 
     On the other hand, according to the can container of the present invention, the longitudinal section of the score line L is an inverted trapezoidal shape comprising the bottom face  5 B. Therefore, even if the domed portion  3 A is deformed little bit outwardly, the bottom face  5 B creates a clearance between the inclined lateral faces  5 A. For this reason, the inclined lateral faces  5 A are not brought into contact with each other immediately so that the score line L will not be ruptured undesirably even if the inner pressure of the can container  1  is raised little bit. As mentioned above, the score line L is ruptured by a slight deformation of the bottom lid  3  if the width of the bottom face  5 B is too narrow, and to the contrary, it is difficult for the score line L to be ruptured if the width of the bottom face  5 B is too wide. For this reason, the width of the bottom face  5 B is preferably within the range from 0.03 mm to 0.1 mm. 
     As also mentioned above, according to the present invention, a planar shape of each score line L is semicircle, and end portions thereof are extended approximately in the radial direction of the can container  1 . Therefore, the semicircular portion enclosed by the ruptured score line L is easy to pop up outwardly when the domed portion  3 A is deformed to protrude outwardly so that the score line L is ruptured, in comparison with the case in which the score line is formed linearly on the bottom lid. For this reason, it is possible to release the inner pressure of the can container  1  promptly. Additionally, since the end portions of the score line L are directed approximately in the radial direction of the can container  1 , the bottom lid  3  will not be fractured partially even if a rupture of the score line L resulting from a rise in the inner pressure of the can container  1  extends beyond the end portion of the score line L so that the bottom lid  3  cracks. To the contrary provided that the end portions of the score line L are directed in the circumferential direction, a propagation of a rupture of the score line L would connect to the end portion of adjoining score line L, in case the score line L is ruptured and such rupture extends beyond the end portion thereof to crack the bottom lid  3 . As a result, a disc shaped fragment of the bottom lid  3  may be separated therefrom. 
     On the other hand, according to the can container of the present invention, the end portions of the score line L are directed approximately in the radial direction of the can container  1 . Therefore, circumferentially situated score lines L are not positioned on the extension of the end portions of the adjoining score line L. For this reason, the bottom lid  3  will not be fractured partially even if a rupture of the score line L extends beyond the end portion thereof and cracks the bottom lid  3 . In addition, according to the present invention, not only the can container in which the bottom lid  3  is seamed with the can body  2 , but also a can container in which a can body and a bottom lid are formed integrally may be used. Moreover, not only an aerosol can but also a bottle-shaped can in which a threaded portion is formed on one of the end portions of the can body  2 . 
     INDUSTRIAL APPLICABILITY 
     This invention can be utilized in the field of manufacturing aerosol cans or cans for manufacturing aerosol cans.