Injection blow molding method

Claim 1

A method of forming biaxially oriented hollow articles from a thermoplastic material, said method comprising the steps of successively: (a) engaging a core rod within an injection mold so that the core rod extends into the cavity of the injection mold and injecting thermoplastic in molten form into the cavity to form a parison around the core rod; (b) maintaining the parison-contacting surfaces of the core rod and injection mold at low temperatures relative to the thermoplastic being processed, this end being effected by circulating low temperature coolant maintained at a temperature within the range of 32°-50° F. therethrough, such that the parison within the injection mold is rapidly cooled to an average bulk temperature at or very near the preferred orientation temperature of the polymer being processed, whereby a temperature gradient is established across the thickness of the parison, the midpoint of the parison being substantially hotter than the outer portions of the parison which are in contract with the cold mold and core rod surfaces; (c) removing the core rod with the parison thereon and subsequently engaging the core rod with a blow mold so that the core rod and the parison extend into the cavity of the blow mold and the neck of the parison is retained in neck ring halves within the cavity mouth of the blow mold; (d) allowing the temperatures within the walls of the parison to equilibrate while the core rod is engaged within the blow mold, such that the temperature at points across the thickness of the parison are uniform, and the average bulk temperature of the parison remains at or near the preferred orientation temperature of the polymer being processed, such constituting a self-equilibrating process in which no external temperature conditioning means are provided to heat or cool the parison still remaining on the core rod; (e) then stretching the major portion of the temperature equilibrated parison in an axial direction by advancing the entire core rod forward, axially into the blow mold, while retaining the neck portion of the parison in a fixed position; (f) radially blowing and expanding the temperature equilibrated parison into intimate contact with the cavity surfaces of the blow mold, at a time not earlier than the commencement of said axial stretching step; and (g) cooling the finished article and removing it from the blow mold when a suitable ejection temperature is achieved.

Claim 2

A method of forming biaxially oriented hollow articles from a thermoplastic material, said method comprising the steps of successively: (a) engaging a core rod within an injection mold so that the core rod extends into the cavity of the injection mold and injecting thermoplastic in molten form into the cavity to form a parison around the core rod; (b) maintaining the parison-contacting surfaces of the core rod and injection mold at low temperatures relative to the thermoplastic being processed, this end being effected by circulating low temperature coolant maintained at a temperature within the range of 32°-50° F. therethrough, such that the parison within the injection mold is rapidly cooled to an average bulk temperature at or very near the preferred orientation temperature of the polymer being processed, whereby a temperature gradient is established across the thickness of the parison, the midpoint of the parison being substantially hotter than the outer portions of the parison which are in contract with the cold mold and core rod surfaces; (c) removing the core rod with the parison thereon and subsequently engaging the core rod with a blow mold so that the core rod and the parison extend into the cavity of the blow mold and the neck of the parison is retained in neck ring halves within the cavity mouth of the blow mold; (d) allowing the temperatures within the walls of the parison to equilibrate while the core rod is engaged within the blow mold, such that the temperature at points across the thickness of the parison are uniform, and the average bulk temperature of the parison remains at or near the preferred orientation temperature of the polymer being processed, such constituting a self-equilibrating process in which no external temperature conditioning means are provided to heat or cool the parison still remaining on the core rod; (e) then stretching the major portion of the temperature equilibrated parison in an axial direction by advancing the entire core rod forward, axially into the blow mold, while retaining the neck portion of the parison in a fixed position; (f) radially blowing and expanding the temperature equilibrated parison into intimate contact with the cavity surfaces of the blow mold, at a time not earlier than the commencement of said axial stretching step; and (g) cooling the finished article and removing it from the blow mold when a suitable ejection temperature is achieved.