DE19515516A1 - Frustrated conical metal insert used in two-stage blow moulding of hollow plastic bottle bases - Google Patents

Abstract

In forming the base of a plastic vessel during blow moulding, a novel frustrated conical (1a, 1b) base insert (1) is used. This has an essentially smooth casing surface (1a) and is used in the first blow moulding stage of a vessel having a hollow, domed base (10). Also claimed is the process producing a plastic bottle, with a base transparent for inspection and capable of being washed in hot water; esp. made of PET. The inward truncated cone is formed in the first blow moulding. When extracted from the mould, or after shrinkage, this has an undulating cross section (10', 10", 10w); the point of inflexion (10w) lies axially higher than the basal resting- or contact ring of the bottle. Also claimed is the equipment to carry out the process.

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. These 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.

The object of the invention is therefore to a floor geometry To provide plastic bottles that both is thermally stable as well as without shadow effects, so is fully inspectable to remove residual lye (from the Cleaning) or foreign bodies in the container safely and reliably, so fully, to be able to recognize before the bottle is filled. 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.

With this solution, the inspection ability is reduced because the one causing the radial retraction of the bottle base Plastic stand is not optically transparent. 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 invention achieves the aforementioned object in three forms, especially by using a truncated cone Soil insert (claim 1) or by a manufacturing process, in which a preform in a first blow molding frusto-conical bottle bottom, which after removal has a wavy cross-section (claim 9) or with a device for carrying out the method mentioned, in which provided a truncated cone bottom in a first blow mold and a second blow mold is essentially one has dome-shaped bottom (claim 11).

The substantially dome-shaped bottom of claim 11 is from the shape of the bottom geometry from the first blow mold removed bottle adapted (claim 16) so that in the second blow molding the floor is only marginally in changed its geometry, only in its fundamental already existing forms is clarified. Identity of form but 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 gets the floor 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 resulting wave structure in the Floor architecture is already the floor design, the full one optical inspection without shadow formation at the same time Temperature stability allowed. This floor geometry is in Cross-section wavy, so it has one to the inside of the bottle directed first curvature r ', the substantially spherical segment is shaped, and a second, outward-facing Curvature r '', which adjoins the first curvature r '.

Radially outside the first curvature is the ground contact ring trained, on which the bottle can stand safely.

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 this can already be wavy Trained floor will still be made clear when on a second blow mold insert is blow molded again. This Blow mold insert has essentially the same design, like the bottom, which is after the first blow molding and the Removing the truncated cone insert forms so that only minor deformations occur (claim 16). One of them can be an arched dome that matches the upper one Plateau region of the truncated cone (claim 8) - shown in Bottom of the bottle - corresponds (claim 17, 7).  

Between the two curvatures of the first Blow molding of the resulting floor is a turning point that is visibly shifted inwards, from which it follows that the the first (outer) curvature is more pronounced than the second (Inner) curvature of the floor geometry. The is accordingly second floor insert, whereas the first Floor insert with its outer surface for the first blow molding is essentially linear (or: flat).

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 can be designed (claim 1), but it can also designed in one piece with the blow mold, the bottom of which it forms be (claim 1, claim 11).

The two-stage blow molding process, which is clearly addressed is concerned with the preform, which in a first blow molding Step into a first mold under pressure Intermediate container is formed. The intermediate container can be significantly larger than the final target container. Of 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 floor remains in his wavy shape mathematically similar to what a through Shrinkage caused dimensional change includes 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 13, 14), 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. Initial 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 base 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 in more detail below 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, after its blow molding on the mold bottom 20 shown in Fig. 2, the wavy geometry 10 ', 10 '', 10 w already recognizable in Fig. 1a here with an unchanged turning point 10 w an illustrated wave geometry 10 'and 10 ''has.

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 illustrates 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 is surprisingly created 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.

Recognizable from the geometry is an architecture which is wavy in cross-section, in which a first, outer curvature 10 'with a radius r' is formed, which is formed inwardly by the 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 disc-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 bottom, 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 (17)

1. Use of a truncated cone-shaped ( 1 a, 1 b) bottom insert ( 1 ) with a substantially flat lateral surface ( 1 a) for the first blow molding of a plastic container with an inwardly directed dome-shaped bottom ( 10 ; 10 ′, 10 ′ ′, 10 k, 10 w, 10 r). 2. Use according to claim 1, in which with a second bottom insert ( 20 ) in a second blow molding the dome-shaped bottom ( 10 ) with a spherical segment (spherical layer; 10 ') with a first radius (r1) and with an upper curvature ( 10 '' ) with a second radius (r2) is more pronounced or reshaped, the curvatures (r1, r2) being directed towards each other. 3. Use according to one of the claims mentioned, in which the first radius (r1) is significantly larger than the second radius. 4. Use according to one of the mentioned claims, in which the jacket ( 1 a) of the truncated cone ( 1 ) has an angle (α) of 40 ° to 70 ° with respect to the bottle axis ( 100 ) ("about 60 °") and is flat . 5. Use according to claim 4, wherein the lateral surface ( 1 b) extends at 60 °. 6. Use according to one of the claims mentioned, in which the Floor insert is metallic. 7. Use according to one of claims 2 to 6, in which with the second bottom insert ( 20 ) of the plateau region ( 1 c) of the first bottom insert ( 10 ) corresponding central floor area ( 10 k) of the bottle bottom is slightly curved. 8. Use according to one of the claims, in which

• (a) the truncated cone base insert ( 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. Manufacturing process for bottom-side inspectable and hot-washable plastic bottles, in particular made of PET, in which

• - In a first blow molding, the bottom region ( 10 ) of the bottle is molded onto an inwardly directed truncated cone ( 1 );
• - The molded truncated cone-shaped bottle bottom after removing it from the mold or shrinking - in cross-section - receives a corrugation ( 10 ', 10 '', 10 w), the turning point ( 10 w) of which is axially higher than the floor-standing ring ( 10 r) Bottle ( 10 ).

10. Manufacturing method according to claim 9, in which the corrugation ( 10 w, 10 ', 10 '') is formed automatically - solely by removing the bottom insert ( 1 ) - whereby the bottom ( 10 ) is substantially free of tension. 11. Device for carrying out the method according to one of claims 9 or 10,

• - In which a plastic preform is formed at an elevated temperature in a first blow mold with a truncated cone bottom ( 1 ; 1 c, 1 a, 1 b) under increased pressure;
• an actuating device is provided which opens the first blow mold in order to enable the intermediate container formed in the first blow mold to shrink;
• - A second blow mold is provided with an essentially dome-shaped bottom ( 20 ; 20 a, 20 b, 20 c, 20 d).

12. The apparatus of claim 11, wherein the one or more bottoms ( 20 ; 1 ) of the blow mold (s) are designed as a metallic insert. 13. The apparatus of claim 11 or 12, wherein the Intermediate container and the finished molded container one storage device each distributed to several are arranged. 14. The apparatus of claim 13, wherein the container is removable are arranged on the respective storage device. 15. The apparatus of claim 11 to 14, wherein the container Bottles are. 16. The device according to any one of claims 11 to 15, wherein the dome-shaped bottom ( 20 ) of the second blow mold is adapted to the bottom geometry of the bottles removed from the first blow mold - or to the bottles formed after shrinking. 17. The apparatus of claim 16, 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).