Surface treated steel strip and manufacturing method of surface treated steel strip

Abstract

A surface treated steel strip according to the present invention includes: a base steel sheet; a zinc phosphate coating film layer made of needle zinc phosphate crystals which are formed in an island shape on a surface of the base steel sheet; and a lubricating coating film layer covering the surface of the base steel sheet and a part of the zinc phosphate coating film layer, and containing at least a lubricating component, in which an area ratio of the zinc phosphate crystals exposed from a surface of the lubricating coating film layer is 25% to 90%.

1 - 8 . (canceled) 
     
     
         9 . A surface treated steel strip, comprising:
 a base steel sheet;   a zinc phosphate coating film layer made of needle zinc phosphate crystals which are formed in an island shape on a surface of the base steel sheet; and   a lubricating coating film layer covering the surface of the base steel sheet and a part of the zinc phosphate coating film layer, and containing at least a lubricating component, wherein   an area ratio of the zinc phosphate crystals exposed from a surface of the lubricating coating film layer is 25% to 90%.   
     
     
         10 . The surface treated steel strip according to  claim 9 , wherein
 the zinc phosphate crystals have an average grain diameter in a major axis direction of 25 μm to 70 μm, and have an average grain diameter in a minor axis direction of 3 μm to 10 μm.   
     
     
         11 . The surface treated steel strip according to  claim 9 , wherein
 a coating weight of the zinc phosphate coating film layer is 1.5 g/m 2  to 15.0 g/m 2  per one side.   
     
     
         12 . The surface treated steel strip according to  claim 10 , wherein
 a coating weight of the zinc phosphate coating film layer is 1.5 g/m 2  to 15.0 g/m 2  per one side.   
     
     
         13 . The surface treated steel strip according to  claim 9 , wherein
 a coating weight of the lubricating coating film layer is 1.0 g/m 2  to 12.0 g/m 2  per one side.   
     
     
         14 . The surface treated steel strip according to  claim 10 , wherein
 a coating weight of the lubricating coating film layer is 1.0 g/m 2  to 12.0 g/m 2  per one side.   
     
     
         15 . The surface treated steel strip according to  claim 11 , wherein
 a coating weight of the lubricating coating film layer is 1.0 g/m 2  to 12.0 g/m 2  per one side.   
     
     
         16 . The surface treated steel strip according to  claim 12 , wherein
 a coating weight of the lubricating coating film layer is 1.0 g/m 2  to 12.0 g/m 2  per one side.   
     
     
         17 . The surface treated steel strip according to  claim 9 , wherein
 the lubricating coating film layer contains an alkali metal silicate whose molar ratio represented by SiO 2 /M 2 O (M is alkali metal) is 2 to 5, and a polymeric wax made of at least either a polyethylene wax or a polypropylene wax having an average grain diameter of 0.1 μm to 3.0 μm; and   a solid content of the alkali metal silicate and a solid content of the polymeric wax with respect to a total solid content mass of the lubricating coating film layer are 60 mass % to 90 mass % and 5 mass % to 40 mass %, respectively.   
     
     
         18 . The surface treated steel strip according to  claim 10 , wherein
 the lubricating coating film layer contains an alkali metal silicate whose molar ratio represented by SiO 2 /M 2 O (M is alkali metal) is 2 to 5, and a polymeric wax made of at least either a polyethylene wax or a polypropylene wax having an average grain diameter of 0.1 μm to 3.0 μm; and   a solid content of the alkali metal silicate and a solid content of the polymeric wax with respect to a total solid content mass of the lubricating coating film layer are 60 mass % to 90 mass % and 5 mass % to 40 mass %, respectively.   
     
     
         19 . The surface treated steel strip according to  claim 11 , wherein
 the lubricating coating film layer contains an alkali metal silicate whose molar ratio represented by SiO 2 /M 2 O (M is alkali metal) is 2 to 5, and a polymeric wax made of at least either a polyethylene wax or a polypropylene wax having an average grain diameter of 0.1 μm to 3.0 μm; and   a solid content of the alkali metal silicate and a solid content of the polymeric wax with respect to a total solid content mass of the lubricating coating film layer are 60 mass % to 90 mass % and 5 mass % to 40 mass %, respectively.   
     
     
         20 . The surface treated steel strip according to  claim 12 , wherein
 the lubricating coating film layer contains an alkali metal silicate whose molar ratio represented by SiO 2 /M 2 O (M is alkali metal) is 2 to 5, and a polymeric wax made of at least either a polyethylene wax or a polypropylene wax having an average grain diameter of 0.1 μm to 3.0 μm; and   a solid content of the alkali metal silicate and a solid content of the polymeric wax with respect to a total solid content mass of the lubricating coating film layer are 60 mass % to 90 mass % and 5 mass % to 40 mass %, respectively.   
     
     
         21 . The surface treated steel strip according to  claim 13 , wherein
 the lubricating coating film layer contains an alkali metal silicate whose molar ratio represented by SiO 2 /M 2 O (M is alkali metal) is 2 to 5, and a polymeric wax made of at least either a polyethylene wax or a polypropylene wax having an average grain diameter of 0.1 μm to 3.0 μm; and   a solid content of the alkali metal silicate and a solid content of the polymeric wax with respect to a total solid content mass of the lubricating coating film layer are 60 mass % to 90 mass % and 5 mass % to 40 mass %, respectively.   
     
     
         22 . The surface treated steel strip according to  claim 14 , wherein
 the lubricating coating film layer contains an alkali metal silicate whose molar ratio represented by SiO 2 /M 2 O (M is alkali metal) is 2 to 5, and a polymeric wax made of at least either a polyethylene wax or a polypropylene wax having an average grain diameter of 0.1 μm to 3.0 μm; and   a solid content of the alkali metal silicate and a solid content of the polymeric wax with respect to a total solid content mass of the lubricating coating film layer are 60 mass % to 90 mass % and 5 mass % to 40 mass %, respectively.   
     
     
         23 . The surface treated steel strip according to  claim 15 , wherein
 the lubricating coating film layer contains an alkali metal silicate whose molar ratio represented by SiO 2 /M 2 O (M is alkali metal) is 2 to 5, and a polymeric wax made of at least either a polyethylene wax or a polypropylene wax having an average grain diameter of 0.1 μm to 3.0 μm; and   a solid content of the alkali metal silicate and a solid content of the polymeric wax with respect to a total solid content mass of the lubricating coating film layer are 60 mass % to 90 mass % and 5 mass % to 40 mass %, respectively.   
     
     
         24 . The surface treated steel strip according to  claim 16 , wherein
 the lubricating coating film layer contains an alkali metal silicate whose molar ratio represented by SiO 2 /M 2 O (M is alkali metal) is 2 to 5, and a polymeric wax made of at least either a polyethylene wax or a polypropylene wax having an average grain diameter of 0.1 μm to 3.0 μm; and   a solid content of the alkali metal silicate and a solid content of the polymeric wax with respect to a total solid content mass of the lubricating coating film layer are 60 mass % to 90 mass % and 5 mass % to 40 mass %, respectively.   
     
     
         25 . A manufacturing method of a surface treated steel strip, comprising
 a thermal refining step of performing thermal refining on a surface of a base steel sheet by utilizing a surface conditioner containing titanium colloid;   a zinc phosphate coating film layer forming step of making needle crystals of zinc phosphate grow in an island shape on the surface of the base steel sheet after being subjected to the thermal refining of surface to form a zinc phosphate coating film layer on the surface of the base steel sheet; and   a lubricating coating film layer forming step of forming a lubricating coating film layer by coating a lubricating treatment agent containing at least a lubricating component to the surface of the base steel sheet and the zinc phosphate coating film layer so that a coating weight of the lubricating treatment agent becomes 1.0 g/m 2  to 12.0 g/m 2  per one side, and making an area ratio of the zinc phosphate crystals exposed from a surface of the lubricating coating film layer to be 25% to 90%.   
     
     
         26 . The manufacturing method of the surface treated steel strip according to  claim 25 , wherein
 the base steel sheet is heated in the zinc phosphate coating film layer forming step.   
     
     
         27 . The manufacturing method of the surface treated steel strip according to  claim 26 , wherein
 the base steel sheet is heated by applying steam to the base steel sheet.