Method and device 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.

Claims

1. A method for producing preforms with an improved neck geometry beneath a threaded region or a transporting ring for a simplified subsequent blow-molding process, wherein the produced preform is made of at least one thermoplastic material and has a significantly thinner wall thickness in a neck region beneath the thread than in the thread itself, and the preform is provided in order to be formed into blow-molded containers, the method comprising: providing at least two channels having an increased wall thickness so that when the preform is injection molded the holding pressure is maintained, despite thin-walled regions, the at least two channels being provided on a circumference of the described preform regions; and designing a mold for the preform so that two or three of the channels are provided over the thin-walled region with a sufficient width to ensure maintenance of pressure in the neck region so that the preform is producible by conventional injection molding technology, 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.

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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a cross section of a preform as is conventionally produced according to the prior art,

(2) FIG. 2 shows a cross section of a preform in which the region beneath the transporting ring has been configured using different methods following or during the injection-molding process in the mold, or in the post-cooling station, and the wall thickness there can thus be decreased more or less as desired,

(3) FIGS. 3-6 show schematic views of the post-cooling unit, in which the embossing elements have been integrated and from which it can be seen how the embossing forces can be applied,

(4) FIG. 7 shows the schematic illustration, as seen from the outside and from the side, of the flow paths on the wound-up preform neck,

(5) FIGS. 8a and 8b show the use of slide inserts for producing relatively thin wall thicknesses in the mold following or during the filling operation, and

(6) FIG. 9 shows a plan view of an example of a production arrangement for preforms.

DETAILED DESCRIPTION OF THE INVENTION

(7) FIG. 1 shows a preform produced according to the prior art. Said preform may have a transporting ring 3 for further container-production steps—it may also be possible in the future, however, to dispense with said transporting ring 3, since it is possible, if appropriate, to grip the region between the ribs of the preform. The wall thickness in the region beneath the transporting ring 3 here has a similar wall thickness 12 as the threaded region 15. On account of the risk of the melt freezing, preforms according to FIG. 2, which are optimized for the blow-molding process by having reduced wall thicknesses 9 beneath the transporting ring 3, can be realized by injection molding only with limited success, since it is then no longer possible for the holding pressure, which counteracts the shrinkage of the preform during the cooling process, to act in the critical regions.

(8) This invention discloses three solution-related approaches as to how the preform in FIG. 2 can be produced. It should be mentioned here, however, that all three methods produce at least two ribs or channels 14 on the circumference of the preform region described, but said ribs or channels have no adverse effect on the desired result. In order for it to be possible, however, for a preform like that shown in FIG. 2 to be produced by conventional injection molding, the mold 17 is configured such that at least two, and even better three, channels 14 of sufficient width, as in FIG. 7, are provided over the thin wall 9 beneath the preform neck 15, said channels ensuring that the holding pressure in the neck region 15 is maintained.

(9) In order to make the channels 14 narrower, however, it is also possible for at least two sliding elements 13 to be integrated in the mold 17, as illustrated in FIG. 8a and FIG. 8b, said sliding elements then being used at the optimum point in time of the injection-molding process. These elements press the still soft polymer material in the mold into regions which are less critical for the blow-molding process and, in doing so, possibly assist the holding-pressure phase.

(10) It is also possible, however, for narrower channels to be achieved following the injection-molding process in that, following initial cooling and opening of the mold 17, they are removed in a conventional manner by a removal arm 18 and said modification is shifted to the subsequent post-cooling phase. The removal arm 18 here has a multiplicity of cooling sleeves 8, in which the preform according to FIG. 1 is introduced as far as the neck region 15.

(11) Both the injection-molding machines with mold 17 and the removal arm 18 are well known from the prior art.

(12) Such a cooling sleeve 8 is illustrated in FIGS. 3 to 6. The initially produced preform according to FIG. 1 has a conventional shape with a relatively thick wall thickness in the region beneath the transporting ring 3 and has its outer body region accommodated, with a virtually full, direct contact, in a water-cooled cooling sleeve 8. There is no need to give any more details relating to this present cooling operation, which uses liquids or gases, since numerous variants are known from the prior art.

(13) The left-hand preforming position illustrated in FIG. 3 shows that the cooling sleeve 8, in the upper region, has embossing elements 5, which are mounted on springs 6 and are secured by screws. The preform 1 has its transporting ring 3 resting on the embossing elements 5 and thus has not yet reached its axial end position in the cooling sleeve 8. If the preform does not have a transporting ring 3, it is then possible, as an alternative, for the preform 1 to be brought into this position by a movable, spring-mounted base support 11 on its domed base. In this position, the embossing elements 5 are not yet in shaping abutment against the preform 1, as a result of which this region can reheat on account of contact cooling being absent. In order to intensify the preform cooling, the number of cooling sleeves 8 may be a multiple of the number of cavities in the mold 17. It is thus possible for the residence time of the preform 1 or preform 2 in the cooling phase to continue for a number of injection-molding cycles.

(14) In order to prepare the mold 17 as quickly as possible for the next injection-molding cycle, a removal arm 18 removes the preforms from the mold region. The removal arm 18 here assumes such a position that the mouth openings of the last-produced number of preforms 1 are located opposite a transporting plate, on which are mounted supporting pins 4 and bell-shaped pressure-exerting members 7 in a number equal to the number of preforms, can be aligned axially. On account of the high level of force which is then required, it is possible for the sake of simplicity for the transporting plate to be mounted directly on the moving platen. However, it could also be an independently movable unit.

(15) The supporting pin 4 is provided essentially so that, when the removal gripper 18 is brought together with the transporting plate, the preform 1 is centered and, during the following embossing operation by the embossing elements 5, deformation of the internal diameter of the preform is for the most part avoided. The embossing operation itself is initiated with the same action of the removal gripper 18 being brought together with the transporting plate, during which the embossing elements 5 are subjected to the necessary force by way of the bell-shaped pressure-exerting element 7. The actual embossing forces are produced by the conical mounting of the embossing elements 5, which thus move by a geometrically predefined displacement amount in relation to the preform axis. The angle and the length of the cone are selected in accordance with the amount of force required for embossing purposes.

(16) The force and the point in time for the actual embossing operation can be defined by a dedicated overall drive of the transporting plate. If the transporting plate, however, is connected directly to the moving platen of the injection-molding machine, it is necessary to use individual axial drives if the point in time for the embossing operation is to be delayed.

(17) During removal, the preforms according to FIG. 1 are mounted in the inner contour of the cooling sleeve 8 such that, although they are indeed capable of executing a further defined-length axial displacement, which is necessary for the following embossing operation, they are prevented from so doing by the embossing elements 5, since the transporting rings 3 rest there. If the preforms do not have any transporting rings 3, then the preform is preferably retained in this defined position by a moveable, resiliently mounted base support 11. This defined residual axial displacement is executed for the embossing operation by the supporting pin 4, the bell-shaped pressure-exerting member 7, the preform 1 and the embossing elements 5, counter to the restoring compression spring 6. In the case of preforms without supporting rings 3, the base support 11 is additionally moved counter to the compression spring 10. The embossing displacement is executed ideally when the heat balance is optimum for embossing as a result of the reheating at the embossing location 9.

(18) The embossing elements 5 can be formed, and positioned, in more or less any desired manner in the shaping region. It is possible for the embossing elements 5 to be all the same size or different sizes. The number of embossing elements can also be selected as desired on an individual basis. An ideal scenario is that where there are three to six equal-size embossing elements 5, which can each leave behind axial ribs 14 at the location where the preform 2 is embossed. If these ribs 14 are distributed uniformly, which is achieved by equal-size embossing elements 5, the subsequent blow-molding process is not disadvantaged.

(19) Once the embossing operation has been completed, the system can be relieved of loading, as a result of which the restoring compression spring moves the embossing elements 5, and thus the preform 2, the bell-shaped pressure-exerting member 7 and the supporting pin 4, into the starting position again. It is, of course, possible for the restoring compression spring 6 to be replaced by a pneumatic function, in which case the preform 2 can be ejected at any desired later point in time via the embossing elements 5. This is critical, in particular, if the preform, for further post-cooling purposes, is to remain with contact cooling in the cooling sleeve 8. In the case of a preform which has no supporting ring 3, it is always possible for the embossing elements 5 to be relieved of stressing, since the preform in this case is not moved axially.

(20) While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.