DE19515516C2 - Process for blow molding a plastic container and device for carrying out the process - Google Patents

Description

The invention is concerned with the design of floor surfaces - called "ground geometry" in this technical field Plastic bottles made from a preform (an injection molding shaped blank) in two blow moldings (introduction of high Pressure). These plastic bottles are hot washable, so they are allowed at a temperature above 60 ° C or 75 ° C not noticeably change in their geometry. The temperature mentioned relates to the temperature of the Washing liquid in which the bottles remain thermally stable have to; minor geometric deformations that affect the mechanical Do not impair stability or stability, can be tolerated.

Most of the time, the plastic bottles are made from PET forms the bottle wall in one or more layers. in the Bottom area, the bottles must stand securely and stable against be inner pressure. This stability affects the Stability. Another stability is mentioned above and concerns the temperature stability when washing the bottle hot, so the requirement of reusability. An additional Property now belongs to the floor area, it must "Inspectable", with which the expert in this technical field the unrestricted visual insight into understands the bottom area in the bottle axis. This Soil inspection must not be affected by shadows and other refractions, because then a visual control of the empty bottle by camera or eye is not possible.

In DE OS 14 79 100 (Dow Chemical) in FIGS. 13 to 16 and the associated description page 8 , last paragraph and 9 first paragraph an approximately frustoconical bottom is described on which a bottle is formed. The bottom of the prior art figures mentioned there is designed so that the bottle retains the bottom geometry of the bottom when it is removed, so that it remains approximately frustoconical. From other prior art documents, DE OS 26 26 848 (Owens-Illionis), AT 368 462 (Solvay), DE 32 43 909 A1 (PLM) and EP 0559 103 A1 (Nissei), floor geometries are also available Bottles known and well known to the expert, which have exactly the shape that the respective bottom of a blow mold gives them and this shape they keep permanently. In the former document, this figure is a step-shaped profiled truncated cone with a gradient extending in the opposite direction at the top of dome section (see FIG. Local Fig. 10), this bottom shape of the bottle does not change more after molding, the concentric through many ring inserts a frusto-like bottom form effect in the long run. The second-mentioned publication also shows in FIG. 1 a stair-shaped bottom of a PET bottle, which is designed to last and which is described as advantageous in its stair-like form, since it can withstand all stresses with this shape. The third document contains a domed mold bottom (there 55 ) for an equally domed bottle bottom (see there Fig. 5, 6). The fourth font has a cylindrically stepped bottom (there 80 c, Fig. 12) for the formation of an equally shaped bottle bottom (there Fig. 13c).

The object of the invention is to provide a base geometry on plastic To provide bottles that are both thermally stable is as well as without shadow effects, so fully is inspectable to residual lye (from cleaning) or Foreign bodies in the container safely and reliably, that is fully recognizable, before the bottle is filled becomes. The invention would like to Inspection ability no restrictions on the bottom diameter take into account how in the prior art such. B. thereby the Case is that bottles an outward, in get and hemispherical bottom geometry extensive retraction in a plastic support ring so that they have a safe footprint.  

The above object is achieved by the invention through the use a truncated cone-shaped bottom insert (claim 1), in which a "preform" in a first blow molding (initially) frustoconical container bottom, which after Removing or detaching a wavy cross section gets. A device for performing the mentioned The procedure involves a truncated cone bottom in a first Blow mold and a second blow mold with one essentially dome-shaped bottom (claim 7).

The essentially dome-shaped bottom is of a shape the bottom geometry of the one taken out of the first blow mold Container adapted (claim 14) so that in the second Blow molding of the bottom of the container is only insignificant changed its geometry, only in its fundamental already existing forms is clarified. "Identity of form" does not mean "dimension identity" (from the dimensions), but design identity (relative location of the partial forms and the partial forms themselves).

The basic architecture of the tank bottom is given after the Remove from the truncated cone-shaped floor insert or after Shrinkage, which causes a detachment from this insert. Surprisingly, it turned out that the after Decreasing / shrinking resulting wave structure in the bottom Architecture is already the floor design, the full optical Inspection without shadow formation with simultaneous temperature Stability allowed. This floor geometry is in cross section wavy, so it has one directed towards the inside of the container first curvature r ', which is essentially spherical segment-shaped, and a second outward curvature r "which is connects to the first curvature r '.

Radially outside the first curvature is the ground contact ring trained, on which the bottle can stand safely. This "Bodenring" is not a separate ring. A separate floor ring would decrease inspection ability because he - than that radial retraction of the bottom part of the bottle  Plastic stand - is not optically permeable. Functional he has such a geometry that - even with his optically permeable design - a shadow-free, full inspection through the floor when not empty would allow.

The surprising effect of the invention is based on the fact that a "memory effect" is used in the linear area of the floor which is the floor after removing the supporting it Truncated cone automatically forms wavy, the bottom becomes essentially free of self-tension.

In a second blow molding (claim 2) this can already wavy container bottom still illustrates be when he's on a second blow mold insert again is blow molded. This blow mold insert has the in essentially the same design as the bottom of the container after the first blow molding and removal from the truncated cone Insert forms so that only slight deformations occur (Claim 14). One of them can be an arched dome be the upper plateau area of the truncated cone - shown in the bottom of the container - corresponds (claim 6, 8, 15).

Between the two curvatures of the first Blow molding resulting container bottom is a Turning point that is recognizably shifted inward, which results shows that the first (outer) curvature is more pronounced is the second (inner) curvature of the floor geometry. The second floor insert is designed accordingly, whereas the first floor insert with its outer surface for the first blow molding is essentially linear (or: even) is designed.

The angle at which the truncated cone is with its Shell surface extends, can be between 40 ° and 70 °, advantageously it runs below 60 ° (claim 4, 5).  

The frustoconical bottom of the first blow mold can be used as Use designed (claim 10), it can also be in one piece be designed with the blow mold, the bottom of which he forms. The two-stage blow molding process, which according to. Claim 2 or Claim 7 is addressed concerns the preform, which in one first blow molding step in a first mold under pressure an intermediate container is formed. The intermediate container can be significantly larger than the final target container. The The intermediate container is shrunk to a size which is below that which is definitely intended. In The shrunk intermediate container is given a second form its final form. Nevertheless, the bottom of the container remains mathematically similar to its undulating shape, which is a dimensional change caused by shrinking, one But maintains design identity.

Both blow molding steps can be designed so that the Bottles or intermediate containers for each blow molding on each a storage wheel are removably arranged (claim 11, 12), so that they can be easily shaped and continuously cooled.

In addition to the surprisingly emerging Fully inspectable floor geometry with a truncated cone first floor also shows the possibility that plastic can be saved. Calculations have shown that up to 10% material can be saved if the container with a linear bottom section corresponding to the truncated cone of the Blow mold bottom is formed and after removal of this floor independently and without further influences in a Floor architecture deformed, which is essentially the one The final bottle later takes shape - after taking an impression on the second floor insert - should receive.  

Elaborate reshaping of the floor geometry to ensure both temperature stability, stability as well full inspection capability without shadow formation are omitted, so that additional curvatures and curls be avoided. An artificial compensation for tension is therefore unnecessary.

The material savings are particularly significant when using the invention the previously thicker bottoms of plastic bottles can be made thinner and still thermal Stability in the floor area is maintained.

The invention is described below with reference to several Exemplary embodiments explained and supplemented.

Fig. 1 is an example of a truncated cone bottom 1 with a linear lateral surface 1 a and a continuously constricting ring constriction area 1 b at the lower end and an upper flat plateau 1 c.

FIG. 1a is the counterpart to FIG. 1. It is a section of a PET bottle extending upwards along the axis 100 , namely the inwardly curved base area 10 , which has a ring contact surface or line 10 at the lower end r has. The outer wall of the bottle, which is not shown here, extends from this contact surface.

FIG. 2 is the second floor insert or the second floor mold 20 , which is dome-shaped or bell-shaped with its surface contour and is closely adapted to the floor architecture 10 shown in FIG. 1a.

FIG. 2a is the bottom geometry of the bottle, according to its blow molding on the imaged in Fig. 2 form the base 20, which in Fig. 1a already recognizable wavy geometry 10 ', 10 ", 10w here at the natural point of inflection 10 w a clarified wave geometry 10' and 10 ".

Fig. 3 represents the prior art in which the mold bottom insert 30 is clearly curved in a dome shape to the bottle in the first blow molding to provide an already very pronounced dome shape.

FIG. 3a represents the base geometry as it is formed after the container removed from the base insert according to FIG. 3 has shrunk and is again blow molded (the second blow molding), the region E being illustrated in FIGS . 3b and 3c.

FIG. 3b,
FIG. 3c illustrate the axial view L along the axis 100 of FIG. 3a and shows a detail of the cross section of Fig. 3a, which is referred to therein with E. Here you can see the shadow formations that arise with the floor geometry, the first blow molding of which is influenced by the floor insert in FIG. 3.

In Fig. 1, an outer surface 1 a is drawn at an angle α with respect to the vertical (the bottle axis 100 ), which extends essentially straight. The mold bottom insert 1 contains at the inner end of the straight surface line a flat plateau 1 c, which runs horizontally. At the lower, outer end of the straight lateral surface 1 a, a ring constriction section 1 b is shown, which is used to execute the ring contact surface 10 r. A first blow molding causes the bottom section of the preform to be pressed onto the truncated cone bottom 1 of FIG. 1. A bottom section which is inclined at an angle α and runs essentially straight, which after shrinking the bottle or pulling the bottle off the bottom according to FIG transforms. 1 in a bottom geometry independently and without external influences, as shown in Fig. 1a. This bottom geometry surprisingly arises due to the release of internal tensions after the first blow molding, the so-called "memory effect" of the preforms after stretch blow molding, which internal stress is generated by the linear, inclined jacket in such a way that the undulating shape is formed.

The geometry shows an architecture which is wavy in cross section, in which a first, outer curvature 10 'with a radius r' is formed, which is formed inwards by the standing bead 10 r or the ring contact surface 10 r.

It ends in a turning point 10 w, from which an oppositely directed curvature 10 "with a smaller radius r" is formed, which leads into a disk-shaped plateau 10 k. The plateau can be flat or slightly arched. The smooth transition from the upper curve r2 to the plateau is achieved via a third curve r3.

With this geometry, an inwardly curved floor is essentially achieved, although the floor insert 1 would be expected to have a completely different floor geometry than is actually the case after substantial compensation of the internal tensions.

Fig. 2 shows a second bottom insert 20 , which is closely adapted in its architecture to the resulting bottom design of the bottle, which is shown in Fig. 1a. Just as in Fig. 1a are also two oppositely directed radii r1 and r2 is present, which define a first curved portion 20 b and an opposite second curved portion 20 a, the latter of which is located radially further inwards than the former. The inner curved region 20 a leads into a slightly domed, stepped dome 20 c, which is adapted to the plateau 10 k of FIG. 1 a in its radial extent. The outer curved region 20 b, which has the shape of a spherical layer, leads into the molded part section, which defines the inner region of the uprising bead 10 r.

The result of the second stretch blow molding process (blow molding process) is shown in FIG. 2a, where the bottom geometry, which was already established in FIG. 1a, is more clearly defined, but is not significantly changed.

The geometries of Figs. 1a, 2a are substantially "similar" (in the mathematical sense).

The last-mentioned floor geometry has an unrestricted ability to inspect, which is indicated by the vertically drawn arrows L - parallel to the central axis 100 . No area of the drawn-in floor, which extends in the radial direction in a wave-like manner (in cross section), shows shadow S. Without shadow, it can be ensured that lye residues or remaining dirt inside the bottle - after hot washing - can be reliably recognized.

The shadow formation S of a prior art is illustrated in FIGS . 3b, 3c, and the area in FIG. 3a that causes this shadow area S — represented as an annular darkening zone in FIG. 3b — is also shown. A camera 40 , which has a lens which is designed such that the entire base area is imaged within the contact ring 10 r, would show the ring according to FIG. 3b as an image. In this area, only a limited visual inspection - a limited possibility of inspection - is justified, so that this floor area does not achieve what can be achieved with the floor area according to FIG. 2b only with the aid of a truncated cone-shaped floor 1 according to FIG. 1.

The counterpart to FIG. 1 is shown in FIG. 3 for illustrative purposes only, with which in the prior art the base region is formed in the first blow molding step, which leads to the base geometry in accordance with FIG. 3a in the second blow molding step. A dominating spherical segment 30 a can be seen there, which occupies almost the entire floor area and gives the floor an architecture that is only curved inward within the standing bead 30 c or 10 r. This dome-shaped structure is first converted into a geometry with a second floor insert (not shown here), which offers thermal stability, mechanical strength but only limited, not optimal inspection capability.

The angle α shown in FIG. 1, which corresponds to the inclination of the lateral surface 1 a of the truncated cone from the vertical, is approximately 60 °; it can easily be changed upwards or downwards, whereby the surprising and independent undulating deformation of the base detached from the truncated cone is still evident. The independent deformation - achieved via the "memory effect" - does not take place outside the areas mentioned.

Claims (15)

1. A method for blow molding a plastic container with an inwardly directed dome-shaped or dome-shaped container bottom ( 10 ; 10 ', 10 ", 10 k, 10 w, 10 r), in which in a first blow molding a preform by introducing high pressure to the Plastic container is deformed, characterized in that a truncated cone-shaped ( 1 a, 1 b) bottom insert ( 1 ) with an essentially flat outer surface ( 1 a) is used for the first blow molding, in order initially to obtain a truncated cone-shaped container base which, after removal or Detachment of the container from the bottom insert ( 1 ; 1 a, 1 b, 1 c) automatically forms a dome or dome ( 10 ). 2. The method according to claim 1, wherein in a second blow molding the dome-shaped or dome-shaped bottom ( 10 ) of the plastic container with a second bottom insert ( 20 ) with a spherical segment ( 10 ') with a first radius (r1) and with an upper curvature ( 10 ") with a second radius (r2) is more clearly shaped or shaped, the two curvatures (r1, r2) being directed towards one another. 3. The method according to claim 2, wherein the post-forming with the second use in which the first radius (r1) is significantly larger than the second radius. 4. The method according to any one of the above claims, wherein the jacket ( 1 a) of the truncated cone ( 1 ) has an angle (α) of 40 ° to 70 ° with respect to the axis ( 100 ) of the plastic container ("about 60 °") and is flat, so that the truncated cone-shaped container bottom is formed accordingly. 5. The method according to claim 4, wherein the outer surface ( 1 a) and accordingly the opposite bottom surface receives a slope that extends at 60 °. 6. The method according to any one of claims 2 to 5, in which with the second bottom insert ( 20 ) of a plateau region ( 1 c) of the first bottom insert ( 10 ) corresponding central floor area ( 10 k) of the container bottom is slightly curved. 7. Device for performing the method according to one of claims 2 to 6, with

• a) a first blow mold with a truncated cone bottom ( 1 ; 1 c, 1 a, 1 b), in which a plastic preform can be formed at an elevated temperature under increased pressure;
• b) an actuator that opens the first blow mold to allow the intermediate container formed in the first blow mold to shrink;
• c) a second blow mold with a substantially dome-shaped bottom ( 20 ; 20 a, 20 b, 20 c, 20 d).

8. The device according to claim 7, wherein

• a) the truncated cone bottom ( 1 ) has a substantially flat or slightly curved plateau region ( 1 c); and or
• b) at the lower end of the lateral surface ( 1 a) a circumferential, inwardly directed shape ( 1 b) is provided.

9. Device according to one of claims 8 or 7, wherein the respective base ( 1 ; 1 a, 1 b, 1 c; 20 ) is metallic. 10. The device according to claim 7, 8 or 9, wherein the one or more bottoms ( 20 ; 1 ) of the blow mold (s) are designed as a metallic insert. 11. The device according to claim 7, wherein the storage devices are provided on which intermediate containers from the first Blow molding and the finished molded container of the second Blow molding are each distributed to several.   12. The apparatus of claim 11, wherein the container is removable are arranged on the respective storage device. 13. The device according to one of claims 9 to 12, wherein the first or second blow mold a bottle-shaped cavity Has. 14. Device according to one of claims 7 to 13, in which a dome-shaped base ( 20 ) of the second blow mold is adapted to the base geometry of the containers removed from the first blow mold - or to the containers formed after shrinking. 15. The apparatus of claim 14, wherein the dome of the second floor ( 20 ) is slightly curved and / or in the lower region a first, outward curvature (r1) and at a slight distance from the dome center ( 20 c), after has an internal curvature (r2).