Patent ID: 8580365

Claim:
A synthetic resin bottle having a gradation pattern in color, obtained by biaxially drawing and blow molding a preform that has been injection molded in a shape of a bottomed cylinder, the synthetic resin bottle comprising: a portion of a cylindrical body of the synthetic resin bottle having a laminar structure in which a main resin layer made of a main resin is laminated with a colored resin layer made of a colored resin of a different color than a color of the main resin; a color-decorated portion defined by the colored resin layer in the portion of the cylindrical body; a color-gradated portion defined by a thin boundary area which is an end portion of the colored resin layer and where the colored resin layer has a gradually reduced thickness in a downward direction; and a non-decorated portion, wherein: the color-gradated portion is located between the color-decorated portion and the non-decorated portion, the thickness of the colored resin layer gradually decreases from the color decorated portion until it reaches the non-decorated portion, the colored resin layer is not present in the non-decorated portion, and the end portion of the colored resin layer is formed using a gradual decrease in the thickness of the colored resin layer caused by the flow behavior of the main resin acting on the colored resin during injection molding of the preform, the colored resin layer is embedded in the main resin layer as an intermediate layer, the preform has a gate imprint at a center of a bottom of the preform, a preform colored resin layer forms a preform intermediate layer in a predetermined height range of the preform and the preform has a color-gradated portion defined by a layer thickness of the preform intermediate layer that is reduced in the downward direction, a change in the layer thickness of the preform intermediate layer in the color-gradated portion is shown by a condition of L/t 1 ≧30 where L is a length of the color-gradated portion and t 1 is the layer thickness at a base of the color-gradated portion, and the preform colored resin layer and the preform intermediate layer form the colored resin layer and the intermediate layer, respectively.