MOLDING TOOL AND METHOD

Description

Field of invention

[0001] The invention relates to a mold for manufacturing a stretch blow-molded polyester bottle and a corresponding method. State of the art

[0002] Stretch blow-molded polyester bottles are manufactured from an injection-molded preform, which already has the bottle neck with an external thread. The bottle body is formed in a blow mold by stretching the preform biaxially within the mold. This is achieved using a blow mandrel.

[0003] It goes without saying that developments aimed at increasing productivity are geared towards shortening bottle production cycle times. The problem is that with short cycle times, a freshly produced PET bottle exhibits the property of reverting to its original preform shape upon cooling. This leads to unreliable bottom molding in serial production. The portion of the bottom that is inwardly formed during stretch blow molding reverts back, shifting from its inner position to its outwardly convex shape as it was in the preform. This retraction of the bottom compromises the bottle's stability.

[0004] This reset effect could be prevented by extending cycle times or improving cooling. However, these measures increase costs and are therefore an undesirable solution.

[0005] US patent 2008 / 0283533 A1 discloses a molding tool with a base that includes a plinth. A projection adjoins the plinth, forming a recess in the container during stretch blow molding. A liquid is filled into the container, and the recess can be filled from the outside with a solid food product.

[0006] US Patent 2015 / 0328825 A1 describes a hot-fill plastic bottle. During stretch blow molding, a base portion of a mold forms the bottom of the container with an inverted bottom section. As the hot product cools, this bottom section inverts upwards to compensate for the vacuum created inside the container during cooling. This prevents uncontrolled deformation of the container.

[0007] US patent 2006 / 0231985 A1 also describes a plastic container with an invertible bottom section. First, the bottom section is formed outwards in the mold. To increase crystallinity, a push rod extends from a base part of the mold and inverts the bottom section inwards. Object of the invention

[0008] The disadvantages of the described state of the art result in the task of creating a polyester bottle that maintains a stable position even with reduced cycle times and is still cost-effective to manufacture. Description

[0009] The problem is solved in a mold for manufacturing a stretch blow-molded polyester bottle by the features specified in the characterizing section of claim 1. Further developments and / or advantageous embodiments are the subject of the dependent claims.

[0010] A base is formed on the bottom section of the mold, projecting into the interior of the mold. The side wall of this base has an angle of inclination of at most 5 degrees to the vertical axis of the mold and is preferably oriented parallel to the vertical axis of the mold. The invention is characterized in that the base projects above the remaining bottom section by a height of between 5 and 7 mm. The base forms a recess in the bottle bottom with a steep side wall. The selected height dimension of the base, between 5 and 7 mm, prevents the recess in the bottle bottom from extending beyond the base's surface, resulting in instability because the polyester's restoring force is insufficient. Additionally, the base stretches the bottle bottom in such a way that the polyester material is further stretched inwards. This further reduces the restoring force, and the reduced polyester material cools down more rapidly.The faster cooling leads to a further reduction in the resilience of the base. The bottle, produced in a short cycle time, therefore has a stable base, as the indentation can no longer bulge outwards beyond the base.

[0011] It has proven advantageous to form the negative mold for the outer part of the bottle base at the lower ends of the first and second mold shells. Since the mold shells are open, the negative molds for the outer bases can be produced more easily than if they were located on the base itself.

[0012] Advantageously, the negative mold for the inner part of the bottle's base is formed on the base adjacent to the side wall. The negative molds are easy to produce because the base is open and the negative molds formed on the mold parts are not formed on the base itself. Another aspect of the present disclosure relates to a polyester bottle produced in the mold described above.

[0013] The invention is also preferably characterized in that the indentation has a side wall which has a side wall angle to the horizontal base of between 60 and 80 degrees, and preferably between 65 and 70 degrees. The side wall angle is slightly less than 90 degrees because the toughness of the polyester does not allow a 90-degree angle to the horizontal to form. However, the resulting side wall angle is sufficiently steep or large that the restoring forces of the indentation are insufficient for it to protrude above the base of the bottle. Despite a cycle time of less than 2 seconds, the bottle therefore has a stable base. In a further particularly preferred embodiment of the invention, the polyester material of the indentation is stretched towards the inside of the bottle by the steep side wall angle. This preferably reduces the restoring force of the indentation.

[0014] Because the steep sidewall angle reduces the restoring forces of the polyester in the indentation, it is impossible for the indentation to regress and bulge out beyond the standing surface.

[0015] Another aspect of the invention relates to a method for manufacturing a polyester bottle in the mold described above. The bottle is produced with a cycle time that is 10% to 20% shorter than the cycle time required for an identical bottle with a conventionally shaped bottom. The reduced cycle time is between 1.8 and 2 seconds. Despite the very short cycle time, the bottle has a stable base.

[0016] Further advantages and features will become apparent from the following description of an exemplary embodiment of the invention with reference to the schematic diagrams. These are shown in a representation not to scale: Figure 1: a sectional view of a molding tool in an open position along the vertical axis and a polyester bottle produced in the molding tool and Figure 2: a detailed view of the bottom of the bottle.

[0017] In the Figure 1 A mold is shown, which is designated in its entirety by reference numeral 11. A polyester bottle 13 is stretch blow-molded in mold 11. The polyester can be PET, PEF, or another bio-based polyester.

[0018] The forming tool 11 has a first and second forming shell 15a, 15b, a retaining plug 17, a stretching mandrel (in the Figure 1(not shown) and a base part 19. The mold shells 15a, 15b and the base part 19 are displaceable between an open and a closed position. In the closed position, a preheated preform is stretched axially by inserting the mandrel and inflated, or radially stretched, by introducing compressed air into the mandrel. The polyester bottle 13 is therefore produced in a known manner by stretching the preform biaxially. After the bottle 13 has been demolded, the mold shells 15a, 15b and the base part 19 are moved into the open position and the bottle 13 is ejected from the mold 11.

[0019] The bottle body 21 is formed in the interior space 29 between the two closed mold shells 15a and 15b. The bottle body 21 is closed at the top by a bottle neck 23, usually with an external thread 25. The bottle neck 23 is injection molded during the production of the preform and remains unchanged during stretch blow molding. The retaining plug 17 is inserted into the bottle neck 23.

[0020] The bottle base 27, which closes the bottle body 21 at the bottom, is formed by the base section 19. A plinth 31, projecting into the interior 29 of the mold 11, is formed on the base section 19. The plinth 31 has a side wall 33, which is preferably parallel to the vertical axis 35 of the mold 11. It is also conceivable that the side wall 33 has a small angle of inclination α of at most 5 degrees to the vertical axis 35.

[0021] The base 39 is formed between the side wall 33 and the lower ends 37a, 37b of the mold shells 15a, 15b. The vertical side wall 33 allows the base 31 to form a recess 41 with a steep side wall 43 on the bottle bottom 27. The side wall angle β is preferably between 65 and 70 degrees, since the tough polyester shrinks slightly after the base 31 forms the 90-degree angle β.

[0022] Due to the 90° inward stretching, the bottle base 27 can no longer bulge outwards, even if the bottle 13 is produced with a very short cycle time, which is between 10% and 20% shorter than the cycle time required for an identical bottle with a conventionally shaped base. The bottle 13 thus has a stable base, as the indentation 41 is always deeper than the base surface 39. At the same time, excess material on the bottle base 27 is stretched further inwards. Due to the forced stretching caused by the base 31, there is also less material present in the area of ​​the bottle base 27. This reduced material cools down rapidly, which further reduces the restoring force of the indentation in addition to the steep sidewall angle β. A base height 45 of 5 to 7 mm is sufficient to create a sufficiently deep indentation 41.

[0023] The outer part 47 of the base 39 is formed at the lower ends of the mold shells 15a, 15b. The negative mold for the inner part 49 of the base 39 of the bottle bottom 27 is formed on the base 31 adjacent to the side wall 33.

[0024] The design of the base 31, in particular its vertical side wall 33, ensures that the indentation 41 never bulges or migrates outwards, even with a very short cycle time. The cycle time is typically 10% to 20% shorter than the cycle time required for an identical bottle with a conventionally shaped base. This allows the polyester bottle 13 to be produced in the mold 11 in a very short time while still maintaining a stable base. Legend:

[0025] 11 Mold 13 Polyester bottle 15a First mold shell 15b Second mold shell 17 Retaining plug 19 Bottom part 21 Bottle body 23 Bottle neck 25 External thread 27 Bottle bottom 29 Interior of the mold 31 Base 33 Side wall of the base 35 Vertical axis 37a Lower end of the first mold shell 37b Lower end of the second mold shell 39 Base surface 41 Indentation 43 Side wall of the indentation 45 Base height 47 Outer part of the base surface 49 Inner part of the base surface α Angle of inclination β Side wall angle

Claims

1. A molding tool (11) for producing a stretch-blow-molded polyester bottle (13) with a bottle neck (23), a bottle body (21), and a bottle bottom (27) from a preform, the molded parts of which can be displaced between an open position and a closed position, comprising - a first and a second mold shell (15a, 15b) within which the bottle body (21) can be molded in the closed position, - a holding stopper (17) which can be inserted into the bottle neck (23), - a blow pin having a compressed-air intake for biaxial stretching of the preform, and - a bottom part (19) which closes the two mold shells (15a, 15b) on the bottom side and which is intended to mold the bottle bottom (27), wherein a base (31) is formed on the bottom part (19), which base projects into the interior (29) of the mold (11) and of which base the side wall (33) has an inclination angle (α) of at most 5 degrees with respect to the vertical axis (35) of the mold (11) and is oriented preferably in parallel with the vertical axis (35) of the mold (11). characterized in that the base (31) projects beyond the remaining bottom part (19) at a height (45) between 5 and 7 mm.

2. A mold according to claim 1, characterized in that the negative form for the outer part (47) of the standing surface (39) of the bottle bottom (27) is formed at the lower ends (37a, 37b) of the first and second mold shell (15a, 15b).

3. The mold according to claim 1 or claim 2, characterized in that the negative mold for the inner part (49) of the standing surface (39) of the bottle bottom (27) is formed on the base (31) following the side wall (33).

4. Process for producing a polyester bottle in the mold according to any of claims 1 to 3, characterized in that the bottle (13) is produced in the mold (11) with a cycle time between 1,8 and 2 seconds.