Method and apparatus for the production of an optimized neck contour on preforms

Abstract

A method and device for producing an optimized neck contour on preforms below the neck which is optimal for subsequent stretch blow molding. The geometry has a significantly thinner wall thickness than the neck itself. The preform can only be produced in the injection molding tool, when axial channels are used on the point or the vanes produce the thin points on the preform during injection molding. The thin-walled geometry on the preform can be produced outside of the mold during post-cooling by embossing. The preform is then removed in a cooled receiving sleeve and is cooled in the body by intensive contact cooling while no cooling contact is made with the preform neck due to the initial position of the embossing element. Due to the reheating of the neck they can be mechanically deformed into a new geometry advantageous for blow molding and thus wall thickness can be influenced.

I claim: 
     
         1 . A method for producing preforms with an improved neck geometry at a transition to a preform body by a reduced cross-sectional area, having a thinner wall thickness interrupted by at least two outer channels beneath a threaded region or a transporting ring for a material and energy-saving blow-molding process, wherein the produced preform made of at least one thermoplastic material, and the preform is provided in order to be formed into blow-molded containers, the method comprising: providing channels having an increased wall thickness similar to an underlying area so that when the preform is injection molded the holding pressure is maintained, despite thin-walled regions that separate the preform body and preform neck, by the channels with an increased wall thickness and the channels with increased wall thickness are always externally visible as a characteristic on a completed preform body. 
     
     
         2 . The method according to  claim 1 , including providing all of the preforms, as the preforms are being produced, with at least two ribs or channels in the thin-walled region beneath the neck. 
     
     
         3 . The method according to  claim 1 , wherein the channels for an injection-molding solution are configured so that, in order for a holding pressure to be maintained, the plastic material in said channels does not freeze any more quickly than the plastic material in the preform neck. 
     
     
         4 . The method according to  claim 1 , wherein, with embossing by pushing, displacement of the plastic material is definable freely in terms of time and is used for holding pressure, and slides produce geometrically predefined ribs in a reproducible manner at parting locations. 
     
     
         5 . The method according to  claim 1 , wherein an embossing operation displaces the plastic material axially into cooling sleeves so that lengthening of the preform is possible. 
     
     
         6 . The method according to  claim 5 , including establishing a temperature range between 90° and 150° at the preform in the region where the embossing takes place. 
     
     
         7 . The method according to  claim 1 , wherein embossing elements of any desired number and size of a geometrically defined contour deform the plastic material of the neck by pulling, pressing and pushing the plastic mass until a volume between the two contours is filled with the plastic material so that the geometry and the wall thickness of the preform neck are defined in a repeatable manner. 
     
     
         8 . The method according to  claim 5 , wherein the embossing operation is determinable freely in terms of time in each part of the process. 
     
     
         9 . The method according to  claim 1 , including, in a multi-cavity application, individually setting an embossing force for each cavity, by mechanical or pneumatic springs for each preform, in order to ensure identical processes. 
     
     
         10 . The method according to  claim 7 , wherein the embossing elements are temperature-controlled or cooled to influence the embossing operation. 
     
     
         11 . The method according to  claim 7 , wherein the embossing elements preform the preform neck for specific bottle-shaped requirements, by pulling, pressing and pushing the plastic material. 
     
     
         12 . The method according to  claim 5 , wherein the embossing operation is preceded by a waiting time of 1 to 20 seconds in order to stabilize heat balance in the preform neck. 
     
     
         13 . An apparatus for production of a preform with a geometry at a transition beneath a neck that is optimized for a blow-molding process, wherein the preform has a considerably thinner wall thickness in a region beneath a thread than in the thread itself, the apparatus comprising: a mold with at least one mold cavity for definitive shaping of the preforms; an injection-molding apparatus that plasticizes raw plastic material to introduce the plastic material into the cavities with the closed mold under pressure, the mold having channels or slides that ensure that a required holding pressure is maintained in the neck despite the reduced wall thickness, or the mold is responsible for the preform geometries in a first shaping step; a removal arm, which is equipped with at least one cooled cooling sleeve, equal in number to the number of cavities, for removing the preforms, the cooling-sleeve having an inner geometry that provides the preform stem, but not the region of the preform neck, with contact cooling; and an embossing apparatus that has embossing elements mounted in a radially floating manner and use a cone to deflect an axial force perpendicularly to an axis and to intensify said force to an extent for an embossing operation that deforms the neck beneath the threaded part by pulling, pressing and pushing operations, said neck being defined by a cavity between the embossing elements and a supporting pin so as to describe the contour and wall thickness of the neck in a repeatable manner. 
     
     
         14 . The apparatus according to  claim 13 , wherein the slide in the mold is also movable under closing pressure. 
     
     
         15 . The apparatus according to  claim 13 , wherein the embossing elements are produced from rigid and thermally conductive material. 
     
     
         16 . The apparatus according to  claim 13 , wherein the embossing elements are cooled or temperature-controlled. 
     
     
         17 . The apparatus according to  claim 13 , wherein the cooling sleeves are liquid-cooled. 
     
     
         18 . The apparatus according to  claim 13 , wherein the embossing elements are mounted resiliently with individually definable spring forces. 
     
     
         19 . The apparatus according to  claim 13 , wherein the embossing elements are seated in a cone that serves as a uniform force-transmitting element. 
     
     
         20 . The apparatus according to  claim 13 , wherein each cooling sleeve with embossing unit has an individual axial drive with preselectable displacement length and forces. 
     
     
         21 . The apparatus according to  claim 13 , wherein the preforms do not have a supporting ring.