Laminate steel sheet for two-piece can, method for production of two-piece can, and two-piece laminate can

Abstract

A laminated steel sheet for a two-piece can body with a high strain level satisfying the following formulae, the polyester resin layer composing the laminated steel sheet having a center line surface roughness (Ra) of 0.2 μm to 1.8 μm: r 1 ≦r , 0.1≦ r 1 /R ≦0.25, and 1.5≦ h /( R−r )≦4 wherein h is the height of the two-piece can body, r is the maximum radius, r 1 is the minimum radius, and R is the radius of the circular laminated steel sheet before forming having the same weight as the can body.

1 . A laminated steel sheet for a two-piece can body satisfying the following formulae, the laminated steel sheet having a polyester resin layer on at least one side, and the surface of the polyester resin layer having a center line surface roughness Ra of 0.2 μm to 1.8 μm:
     r   1   ≦r,  0.1 ≦r   1   /R≦ 0.25, and 1.5 ≦h /( R−r )≦4   wherein h is the height of the two-piece can body, r is the maximum radius, r 1  is the minimum radius, and R is the radius of the circular laminated steel sheet before forming having the same weight as the can body.   
   
   
       2 . The laminated steel sheet for a two-piece can body according to  claim 1 , wherein the surface of the polyester resin layer has a 60 degree glossiness of 30 to 100. 
   
   
       3 . The laminated steel sheet for a two-piece can body according to  claim 1 , wherein the polyester resin layer is formed by the condensation polymerization of a dicarboxylic acid component composed mainly of terephthalic acid with a diol component composed mainly of ethylene glycol, the dicarboxylic acid component comprises from 8 to 20 mol % of an isophthalic acid component as the copolymerization component, the polyester resin layer has a plane orientation factor of 0.04 or less and a crystallization temperature of 140 to 160° C. 
   
   
       4 . The laminated steel sheet for a two-piece can body according to  claim 1 , wherein the surface of the polyester resin layer has a center line surface roughness Ra of 0.2 μm to 1.0 μm. 
   
   
       5 . The laminated steel sheet for a two-piece can body according to  claim 1 , wherein the surface of the polyester resin layer has a center line surface roughness Ra of 0.4 μm to 1.8 μm. 
   
   
       6 . The laminated steel sheet for a two-piece can body according to  claim 5 , wherein the surface of the polyester resin layer has a center line surface roughness Ra of 0.4 μm to 1.0 μm. 
   
   
       7 . A method for making a two-piece can body, comprising multistep forming of a circular blank made of the laminated steel sheet for a two-piece can body according to  claim 1 , thereby obtaining a formed body satisfying the following formulae:
     r   1   ≦r,  0.1 ≦r   1   /R≦ 0.25, and 1.5 ≦h /( R−r )≦4   wherein h is the height of the two-piece can body, r is the maximum radius, r 1  is the minimum radius, and R is the radius of the circular laminated steel sheet before forming having the same weight as the can body.   
   
   
       8 . The method for making a two-piece can body according to  claim 7 , which further comprises heat treatment at a temperature of 150° C. to 220° C. during the forming step. 
   
   
       9 . The method for making a two-piece can body according to  claim 8 , wherein the heat treatment is carried out during the forming step so as to satisfy the following formulae:
     r   1   ≦r,  0.2 ≦r   1   /R≦ 0.5, and 1.5 ≦h /( R−r ) 2.5   wherein h is the height of the two-piece can body, r is the maximum radius, r 1  is the minimum radius, and R is the radius of the circular laminated steel sheet before forming having the same weight as the can body.   
   
   
       10 . The method for making a two-piece can body according to  claim 8 , wherein the heat treatment is carried out several times. 
   
   
       11 . A two-piece can body produced by the method according to  claim 7 .