Method for blow molding plastic articles

Abstract

A method of blow molding plastic articles in two blowing stages. A freely extruded pendant tubular parison is first blown into a pre-form, then the pre-form, while at the temperature most conductive to orientation, is blown to its final configuration. By performing certain operations on the pre-form prior to the final blowing step, improved products can be made. For example, by pinching shut a portion of the pre-form, handled containers can be made on a free extrusion blow molding machine. By stretching the pre-form prior to final blowing, containers of increased top-load or stacking capabilities can be made. .Iadd. This application is a re-issue of U.S. Pat. 3,781,395, issued Dec. 25, 1973, matured from U.S. Pat. application Ser. No. 110,685, filed January 28, 1971. .Iaddend.

I claim: 
     
       1. In a method of making a blown container having an integral handle located at a shoulder of the container and at least partially encompassing an adjacent hand hole, the steps of extruding a freely pendant tube of a diameter substantially less than the transverse dimension of the handled portion of said container, enclosing the tube interiorly of a pre-form mold, blow molding the tube interiorly of said pre-form mold into a pre-form having a localized handle-encompassing portion at the location of the shoulder of the container which portion has a transverse extent which is less than the outside extent of the handle and larger than the outside extent of the hand hole, simultaneously enclosing the blow pre-form in a final blow mold and pinching shut an interior part of the pre-form handle encompassing portion (1) to define the hand hole inwardly of the exterior of said portion and (2) to interpose a tubular hand hole encompassing portion between the pinched hand hole and the outer wall of the final blow mold cavity, and blow molding the pre-form, including the tubular hand hole encompassing portion thereof, interiorly of said final blow mold to form the final blown container. 
     
     
       2. The method as defined in claim 1, wherein the final two steps of the method are carried out after the previously blown pre-form has been chilled internally of the preform blow mold to an average wall temperature most conducive to biaxial orientation of the thermoplastic material during the performance of the final blow molding step. 
     
     
       3. In the method of blow molding a container from a thermoplastic material, the steps of sequentially (1) extruding a tubular parison, (2) pinching the parison shut, (3) blowing the pinched parison internally of a pre-form blow mold into a pre-form (4) cooling the pre-form during the performance of step (3) and thereafter to a temperature conducive to orientation (5) stretching the blown pre-form .Iadd.while at a temperature conducive to orientation.Iaddend., and (6) blowing the .Iadd.stretched .Iaddend.pre-form internally of a final blow mold into the final container .Iadd., while said pre-form is at a temperature conducive to orientation, for biaxially orienting the thermoplastic material. .Iaddend. 
     
     
       4. A method as defined in claim 3, wherein the step of stretching is carried out interiorly of a final blow mold .[., and both steps of stretching and blowing the stretched pre-form are carried out while the pre-form is at a temperature conducive to orientation of the thermoplastic material.].. 
     
     
       5. The method of claim 4, wherein the step of stretching is carried out by inserting an elongated blow tube into the interior of the pre-form, moving the blow tube and the pre-form portion engaged thereby interiorly of the final blow mold, and then blowing the .Iadd.stretched .Iaddend.pre-form by air introduced through the blow tube. 
     
     
       6. The method of claim 4, wherein the step of stretching is carried out by engaging pinching elements with the pre-form, moving the pinching elements relative to the blow mold to stretch the pre-form interiorly of the final blow mold, and then blowing the stretched pre-form. 
     
     
       7. In a method of blow molding a container from a thermoplastic parison, the steps of blowing said parison into a pre-form having a neck portion surmounting a blown body portion, suspending the pre-form from its neck portion, the pre-form being cooled during blowing and thereafter to a temperature conducive to orientation of the thermoplastic material, then engaging a portion of the blown pre-form portion remote from said neck portion, moving the engaged blown portion of said pre-form in a direction away from the neck to stretch the pre-form .Iadd.while at a temperature conducive to orientation.Iaddend., and then blowing the stretching pre-form to the final configuration of the container body.Iadd., while at a temperature conducive to orientation of the thermoplastic material. .Iaddend. 
     
     
       8. The method as defined in claim 7, wherein the pre-form is suspended in a blow mold, and the steps of engaging and moving are both carried out interiorly of said blow mold. .Iadd. 9. In the method of blow molding a container from a thermoplastic material, the steps of sequentially (1) extruding a tubular parison, (2) pinching the parison shut, (3) blowing the pinched parison internally of a pre-form mold into a pre-form, (4) bringing the pre-form to a temperature within the orientation temperature range of the thermoplastic material during the performance of step (3) and thereafter, (5) stretching the blown pre-form while at a temperature conducive to orientation, and (6) blowing the stretched pre-form internally of a final blow mold into the final container while said pre-form is at a temperature conducive to orientation for biaxially orienting the thermoplastic material. .Iaddend..Iadd. .Iadd.10. The method as defined in claim 9, wherein Step (1) is characterized by continuously extruding a tubular parison. .Iaddend. .Iadd.11. The method as defined in claim 9, wherein the pre-form is generally cylindrical having a major axis and a minor axis and Step (5) is characterized by stretching the pre-form in the direction of the major axis for axially orienting the thermoplastic material. .Iaddend. .Iadd. 12. In a method of blow molding a container from a parison of thermoplastic material, the steps of blowing said parison into a pre-form having a neck portion surmounting a blown body portion, suspending the pre-form from its neck portion, bringing the temperature of the blown pre-form during the performance of the blowing step and thereafter to a temperature conducive to orientation of the thermoplastic material, then engaging a portion of the blown pre-form portion remote from said neck portion, moving the engaged blown portion of said pre-form in a direction away from the neck to stretch the pre-form while at a temperature conducive to orientation, and then blowing the stretched pre-form to the final configuration of the container body, while at a temperature conducive to orientation. .Iaddend.