Patent ID: 6906290

Claim:
A method of heating a preform, whereby the preform (P) which has been injection molded into a cylindrical shape with a bottom and is made of a polyethylene terephthalate resin is heated by heat sources ( 1 ) in order to be biaxially stretched and blow molded into a bottle shape, comprising the steps of sequentially executing the following processes to said preform (P): a first heating process (a) to set said heat sources ( 1 ) into a high power state while blowing out cooling air (e) to said preform (P) and quickly heat the preform (P) until a temperature (Ta) of an outer surface of said preform (P) is equal to a temperature value which is slightly lower than a crystallization temperature of said polyethylene terephthalate resin; a temperature adjusting process (b) to leave the preform (P) until a temperature difference (s) between the outer surface temperature (Ta) and an inner surface temperature (Tb) of said preform (P) is equal to or less than a predetermined value in a state where the heating by said heat sources ( 1 ) and the cooling by said cooling air (e) are not executed; and a second heating process (c) to heat the preform (P) after completion of said temperature adjusting process (b) by said heat sources ( 1 ) until the outer surface temperature (Ta) of said preform (P) is equal to a temperature value which is slightly lower than the crystallization temperature of the polyethylene terephthalate resin while blowing out the cooling air (e) to the preform (P), wherein said temperature difference (s) at the end of said temperature adjusting process (b) is set to a value which is equal to or less than a predetermined value in which the inner surface temperature (Tb) of said preform (P) at the end of said second heating process (c) is equal to a temperature value in which an inappropriate stretching is not occurred on the inner surface side of said preform (P).