Bottle-shaped can manufacturing method and bottle-shaped can

Abstract

A method for manufacturing a bottle-shaped can for holding content having strong metal corrosive properties such as sparkling wine. The method includes shaping a cap into a diametrically reduced bottomed cylindrical can body, forming a shoulder portion and a container mouth on the can body, forming a curled portion, a thread and an annular bead on the container mouth, seaming a can lid to the can trunk, and amorphizing a thermoplastic resin layer covering an inner surface of the container mouth on which the curled portion, the thread and the annular bead are formed.

1 . A bottle-shaped can manufacturing method, comprising:
 a cup shaping step of forming a cup by punching out from a metal sheet in which a thermoplastic resin coating layer is formed on at least a surface to be an inner face of the can and a lubricant is applied thereto;   a can trunk shaping step of shaping the cap into a diametrically reduced bottomed cylindrical can body;   a container mouth shaping step of forming a shoulder portion and a container mouth by diametrically reducing one of the end portions of the bottomed cylindrical can body;   a curling/threading/beading step of forming a curled portion on a leading end of the container mouth, and forming a thread and an annular bead on the container mouth; and   an amorphization step of amorphizing at least the thermoplastic resin coating layer covering an inner surface of the can body in which the curled portion, the thread and the annular bead are formed on the container mouth situated above the shoulder portion, by heating at least the thermoplastic resin coating layer covering the inner surface of the can body to above a melting point thereof, and immediately cooling the heated thermoplastic resin coating layer.   
     
     
         2 . The bottle-shaped can manufacturing method as claimed in  claim 1 ,
 wherein the container mouth shaping step includes a top dome shaping step of forming the shoulder portion and the container mouth by diametrically reducing a bottom side of the bottomed cylindrical can body; and   wherein the amorphization step includes a step of amorphizing at least the thermoplastic resin coating layer covering the inner surface of the can body in which the container mouth is opened and a bottom lid is seamed to a lower end of the can trunk on the side opposite to the container mouth.   
     
     
         3 . The bottle-shaped can manufacturing method as claimed in  claim 1 , wherein the amorphization step includes:
 an induction heating step of letting the can body through an induction heating apparatus while rotating the can body around an axis of the can; and   a cooling step of immediately cooling the heated container mouth by immersing the container mouth into a cooling water held in a cooling tank.   
     
     
         4 . The bottle-shaped can manufacturing method as claimed in  claim 3 ,
 wherein the cooling step includes a step of cooling the container mouth by immersing the container mouth into the cooling water held in the cooling tank while orienting the container mouth downwardly; and   wherein the amorphization step includes a blowing step of blowing off the water adhering to the container mouth oriented downwardly.   
     
     
         5 . The bottle-shaped can manufacturing method as claimed in  claim 3 ,
 wherein the amorphization step includes a cooling step of cooling container mouth of the can body conveyed in a manner to orient the container mouth downwardly, by immersing the container mouth into the cooling water held in the cooling tank while inclining a center axis of the container mouth with respect to a water surface, and   thereafter pulling the container mouth out of the cooling tank while inclining the container mouth inversely to that of the case of immersing the container mouth into the cooling water.   
     
     
         6 . The bottle-shaped can manufacturing method as claimed in  claim 3 ,
 wherein the amorphization step includes a cooling step of cooling container mouth while circulating the cooling water in the tank at a substantially same speed as a conveying speed of the can body and in the same direction as a conveying direction of the can body.   
     
     
         7 . A bottle-shaped can, that is formed from a metal sheet in which a thermoplastic resin coating layer is formed on at least a surface to be an inner face of the can,
 wherein a crystallinity (Cn) of the thermoplastic resin coating film covering an inner surface of a container mouth of the finished can satisfies a following inequality (1):
     Cn< 1  (1);
 
   where Cn is an infrared absorption intensity measured by IR spectroscopy method (reflection infrared spectroscopy method), which can be expressed by a following expression:
     Cn =(a peak height at 1340 cm −1 )/(a peak height at 1578 cm −1 ). 
   
     
     
         8 . The bottle-shaped can as claimed in  claim 7 ,
 wherein a relation between the crystallinity (Cn) of the thermoplastic resin coating film at the inner surface of the container mouth of the finished can, and a crystallinity (Cw) of the thermoplastic resin coating film at an inner surface of the can trunk satisfy a following inequality (2):
     Cn/Cw< 1  (2);
 
   where Cw is an infrared absorption intensity measured by the IR spectroscopy method (reflection infrared spectroscopy method), which can be expressed by a following expression:
     Cw =(a peak height at 1340 cm −1 )/(a peak height at 1578 cm −1 ). 
   
     
     
         9 . The bottle-shaped can as claimed in  claim 7 ,
 wherein the thermoplastic resin coating layer covering an inner surface of the container mouth is subjected to an amorphization treatment to amorphize the thermoplastic resin after forming the container mouth, by heating the thermoplastic resin coating layer to above a melting point thereof, and immediately cooling the heated thermoplastic resin.