Flat container comprising thermoplastic resin and method for molding the same

Abstract

The invention realizes easy manufacturing of a flat container molded by blow molding, in which the wall thickness of a container wall is made uniform, and which provides improved mechanical strength, heat resistance, etc. and has a good appearance. The flat container obtained by the blow molding of a polyester resin is characterized in that the container has a flatness ratio of not less than 1.3, and in that its body has a wall thickness ratio of a maximum wall thickness to a minimum wall thickness of not more than 1.6, a difference in elongation between a maximally stretched portion and a minimally stretched portion of not more than 150% in a tensile test at 95° C., a crystallinity of not less than 30%, and a difference in TMA non-load change between a maximally stretched portion and a minimally stretched portion of not more than 500 μm at 75° C. and 100° C.

What is claimed is: 
     
         1 . A two-stage blow molding process of a flat container, the process comprising:
 subjecting a bottomed parison, which is a first intermediate molded article formed from a thermoplastic resin, to primary blow molding to form the first intermediate molded article into a second intermediate molded article having a diameter larger than the minor axis of a cavity within a mold for secondary blow molding,   causing the second intermediate molded article to undergo thermal shrinkage, thereby to form the second intermediate molded article into a third intermediate molded article having a body diameter smaller than the major axis of the cavity within the mold for secondary blow molding and larger than the minor axis thereof,   attaching the third intermediate molded article to the interior of the mold for secondary blow molding subjected to mold surface treatment in an upper portion and/or a lower portion of a body molding surface thereof at least on the long-side side of a container in order to ensure that the third intermediate molded article is slippery when the third intermediate molded article comes into contact,   performing mold clamping, with the third intermediate molded article depressed in the minor axis direction of a mold cavity, and then   performing secondary blow molding.   
     
     
         2 . A two-stage blow molding process of a flat container, the process comprising:
 subjecting a bottomed parison, which is a first intermediate molded article formed from a thermoplastic resin, to primary blow molding to form the first intermediate molded article into a second intermediate molded article having a diameter larger than the minor axis of a cavity within a mold for secondary blow molding,   causing the second intermediate molded article to undergo thermal shrinkage, thereby to form the second intermediate molded article into a third intermediate molded article having a body diameter smaller than the major axis of the cavity within the mold for secondary blow molding and larger than the minor axis thereof,   attaching the third intermediate molded article to the interior of the mold for secondary blow molding, which has convexities formed in an upper portion and/or a lower portion of a body molding surface thereof at least on the long-side side of a container,   performing mold clamping, with the third intermediate molded article depressed in the minor axis direction of a mold cavity, and then   performing secondary blow molding.   
     
     
         3 . A two-stage blow molding process of a flat container, the process comprising:
 subjecting a bottomed parison, which is a first intermediate molded article formed from a thermoplastic resin, to primary blow molding to form the first intermediate molded article into a second intermediate molded article having a diameter larger than the minor axis of a cavity within a mold for secondary blow molding,   causing the second intermediate molded article to undergo thermal shrinkage, thereby to form the second intermediate molded article into a third intermediate molded article having a body diameter smaller than the major axis of the cavity within the mold for secondary blow molding and larger than the minor axis thereof,   attaching the third intermediate molded article to the interior of the mold for secondary blow molding subjected to mold surface treatment in an upper portion and/or a lower portion of a body molding surface thereof at least on the long-side side of a container in order to ensure that the third intermediate molded article is slippery when the third intermediate molded article comes into contact, and which has convexities formed in an upper portion and/or a lower portion of a body molding surface thereof at least on the long-side side of a container,   performing mold clamping, with the third intermediate molded article depressed in the minor axis direction of a mold cavity, and then   performing secondary blow molding.   
     
     
         4 . The flat container two-stage blow molding process according to  claim 1 , wherein the mold surface treatment is coating with a fluororesin. 
     
     
         5 . The flat container two-stage blow molding process according to  claim 3 , wherein the mold surface treatment is coating with a fluororesin. 
     
     
         6 . The flat container two-stage blow molding process according to  claim 4 , wherein the fluororesin is a tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA) or polytetrafluoroethylene (PTFE). 
     
     
         7 . The flat container two-stage blow molding process according to  claim 5 , wherein the fluororesin is a tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA) or polytetrafluoroethylene (PTFE). 
     
     
         8 . The flat container two-stage blow molding process according to  claim 2 , wherein the size of convexities formed on a mold surface is such that the lateral width thereof is 30 to 90% of the major axis of a mold cavity surface, the longitudinal width thereof is 1 to 30% of the formed height of a flat product on the mold cavity surface, and the height thereof is 2 to 40% of the minor axis of the mold cavity surface. 
     
     
         9 . The flat container two-stage blow molding process according to  claim 3 , wherein the size of convexities formed on a mold surface is such that the lateral width thereof is 30 to 90% of the major axis of a mold cavity surface, the longitudinal width thereof is 1 to 30% of the formed height of a flat product on the mold cavity surface, and the height thereof is 2 to 40% of the minor axis of the mold cavity surface. 
     
     
         10 . The flat container two-stage blow molding process according to  claim 1 , wherein the thermoplastic resin is a polyester resin or polyethylene terephthalate. 
     
     
         11 . The flat container two-stage blow molding process according to  claim 2 , wherein the thermoplastic resin is a polyester resin or polyethylene terephthalate. 
     
     
         12 . The flat container two-stage blow molding process according to  claim 3 , wherein the thermoplastic resin is a polyester resin or polyethylene terephthalate. 
     
     
         13 . A method for manufacturing a flat container by the two-stage blow molding process, the method comprising:
 subjecting a bottomed parison preformed from a polyester resin to primary blow molding, thereby molding the bottomed parison into a bottomed cylindrical body having a diameter larger than the minor axis of a cavity within a mold for secondary blow molding, thereafter   causing the bottomed cylindrical body to shrink in a heated condition, thereby to cause the bottomed cylindrical body to maintain a diameter which is smaller than the major axis of the cavity within the mold for secondary blow molding and larger than the minor axis thereof,   attaching the bottomed cylindrical molded article to the interior of the mold for secondary blow molding,   performing mold clamping, with the bottomed cylindrical molded article depressed in the minor axis direction of the cavity within the mold,   feeding thereafter a pressure fluid into the bottomed cylindrical molded article, and   causing the bottomed cylindrical molded article to flow in a heated condition along the shape of the cavity on an inner surface of the mold, thereby to mold the flat container.