STRETCH BLOW MOLDING PROCESS

Abstract

A stretch blow molding process for producing a plastic container from a preform, having an elongated, tubular preform body, extending along a center axis. The first end of the preform body is closed by a preform bottom and the second end is adjoined by a neck part with a pouring opening. A wall, bounds an interior space of the preform. The preform body is heated and introduced into a cavity of a blow mold. A stretching mandrel enters the preform until the stretching mandrel tip reaches the preform bottom. The preform body and the preform bottom are stretched by the stretching mandrel. The preform body and the preform bottom are deformed by introducing a fluid into the preform under pressure. The stretching mandrel makes contact with the inner side of the wall in the region of the preform body.

Claims

1. A stretch blow molding process for producing a plastic container from a preform, comprising: providing a preform having an elongated tubular preform body, which extends along a central axis of the preform and has a first end and a second end essentially opposite the first end, wherein the first end is closed by a bottom of the preform and a neck part with a spout opening is connected to the second end, and having a wall bordering an interior space of the preform and having an inside and an outside; heating the body of the preform to at least 70 C.; inserting the preform into a cavity in a blow molding mold; inserting a stretching mandrel comprising a stretching mandrel body and a stretching mandrel tip into the preform until the stretching mandrel tip reaches the preform body; stretching the body of the preform and the bottom of the preform with the stretching mandrel in the cavity, shaping the preform body and the bottom of the preform according to the cavity by introducing a fluid into the preform under pressure; contacting an inside of the wall in an area of the preform body in at least one predetermined partial area with the stretching mandrel, while it is being inserted into the preform, until it reaches the bottom of the preform.

2. The stretch blow molding process of claim 1, wherein the stretching mandrel body comprises an outside with an exterior contour, so that the inside of the wall of the preform is contacted by the outside of the stretching mandrel body on at least two partial areas extending essentially along the central axis of the preform, so that they are essentially opposite one another with respect to the central axis of the preform, while the stretching mandrel is being inserted into the preform.

3. The stretch blow molding process of claim 2, wherein the stretching mandrel body comprises at least one groove extending essentially as far as the tip of the stretching mandrel or into the tip of the stretching mandrel, the at least one groove configured so that the fluid can be introduced from the spout opening in the preform up to the bottom of the preform when the stretching mandrel has stretched the preform body and the bottom of the preform into the cavity as far as an inside wall of the cavity.

4. The stretch blow molding process of claim 1, wherein, the stretching mandrel extends along a central axis of the stretching mandrel, an extent of the stretching mandrel body at a right angle to the central axis of the stretching mandrel is at least as large in an area adjacent to the stretching mandrel tip as is the extent of the interior space of the preform at a right angle to the central axis of the preform in an area of the body of the preform connected to the bottom of the preform body in an unstretched state of the preform body, and the extent of the interior space is less than 7 millimeters.

5. The stretch blow molding process of claim 1, wherein the stretching mandrel, while being inserted into the preform, widens the preform body.

6. The stretch blow molding process of claim 1, wherein before the stretching mandrel is inserted into the preform, the inside of the wall has a temperature at least 10 C. higher in an area of the preform body than the outside of the wall in the area of the preform body, wherein the inside of the wall in the area of the preform body is at a temperature of at least 100 C.

7. The stretch blow molding process of claim 1, wherein the preform body before being heated is at a temperature of less than 40 C.

8. The stretch blow molding process of claim 1, wherein the stretching mandrel comprises at least one of a heat-insulating layer or an adhesion-reducing layer on an outside thereof.

9. The stretch blow molding process of claim 1, wherein an outside of the stretching mandrel or the inside of the wall of the preform comprises a plurality of webs running in an area of the preform body along an insertion direction, establishing contact between the stretching mandrel and the preform during insertion of the stretching mandrel.

10. The stretch blow molding process of claim 1, wherein the fluid is inserted through the tip of the stretching mandrel.

11. The stretch blow molding process of claim 1, wherein the stretching mandrel is heated outside of the blow molding mold before insertion into the preform.

12. The stretch blow molding process of claim 1, wherein the tip of the stretching mandrel travels a distance between 20 and 200 millimeters while the preform body and the bottom of the preform are being stretched into the cavity by the stretching mandrel.

13. The stretch blow molding process of claim 1, wherein when the stretching mandrel has stretched the preform body and the bottom of the preform into the cavity as far as the wall thereof, the stretching mandrel is essentially in the form of a cylinder at least up to the spout opening of the stretched preform.

14. The stretch blow molding process of claim 4, wherein an extent of the interior space is less than 6 millimeters.

15. The stretch blow molding process of claim 4, wherein an extent of the interior space is less than 5 millimeters.

16. The stretch blow molding process of claim 4, wherein an extent of the interior space is less than 3 to 4 millimeters.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0136] Shown in schematic diagrams, not drawn to scale:

[0137] FIG. 1 shows a preform in a longitudinal section;

[0138] FIG. 2 shows the preform according to FIG. 1 with a stretching mandrel contacting the preform uniformly;

[0139] FIG. 3a shows the preform according to FIG. 1 with a stretching mandrel according to the prior art spaced a uniform distance away from the preform;

[0140] FIG. 3b shows the preform according to FIG. 1 with a stretching mandrel according to the prior art, contacting the preform irregularly; and

[0141] FIG. 4 shows various types of stretching mandrels.

EMBODIMENT OF THE INVENTION

[0142] The invention is explained as an example below on the basis of the drawings. FIG. 1 shows a preform which is designed to be processed further in a stretch blow molding process to form a plastic container. FIGS. 2, 3a and 3b show the preform from FIG. 1 as well as one stretching mandrel inserted into each preform and these figures are used to illustrate the stretch blow molding process.

[0143] With reference to FIG. 1, the preform 11 has a preform body 21 and a neck part 31 connected thereto. The central axis 12 of the preform 11 runs through a first end 23 and a second end 25 of the preform body 21, wherein the first end 23 of the preform body 21 is closed by a bottom 23 of the preform 11. The neck part 31 has a spout opening 35 and is connected to the second open end 25 of the preform body 21.

[0144] With the proposed preform 11, the maximum distance of the inside 17 of the preform wall 13 from the central axis 12 amounts to less than 3.5 or 3 or 2.5 millimeters for a length of the central axis 12 of at least 20, 30 or 50 millimeters. However, the dimensioning is not obligatory.

[0145] Additional advantageous features of the preform 11 include, as shown in FIG. 1, a thread 37 and a supporting ring 39 on the neck part 31. The thread 37 allows later application of a cover (not shown) to the spout opening of the plastic container to be provided from the preform 11. The support ring 39 facilitates the handling of the preform 11 which is provided in particular in the case of a two-stage injection stretch blow molding process (two-step injection stretch blow molding process) such as that provided for production of the preform 11 and the plastic container (from the preform), which brings advantages. In such a two-stage process, the preform 11 is cooled to room temperature after being produced and then is processed further in a stretch blow molding process to form a plastic container only at a later point in time. The preform 11 is produced in one piece by injection molding from a polyester, and this is also true of the thread 37 and the supporting ring 39, which are arranged on the outside 15 of the wall 13 of the preform 11. Like the preform body 21, the neck part 31 also has a first end 33 and a second end 35, wherein the first end 33 of the neck part 31 is connected to the second end 25 of the preform body 21, and the second end 35 of the neck part 31 has the spout opening. The latter leads into the interior space 19 of the hollow preform 11, wherein the interior space 19 extends from the spout opening to the bottom of the preform 11. The interior space 19 is bordered by the inside 17 (i.e., the inner surface) of the wall 13, which also has an outside 15 (i.e., an outer surface). The distance between the inside 17 and the outside 15 is the wall thickness. This may optionally be greater on the average in the area of the preform body 21 than in the area of the neck part 31, wherein structures on the outside 15 of the wall 13 such as the thread 37 and the supporting ring 39 are to be disregarded in evaluating the wall thickness. Normally in production of a plastic container from a preform 11, namely only the preform body 21 is stretched and blow molded, which is why more material is needed in this area. The interior space 19 may optionally have a larger cross section in the area of the neck part 31 than in the area of the preform body 21, wherein the cross section is understood to refer to the cross-sectional area at a right angle to the central axis 12. The central axis 12 of the preform 11 runs from the spout opening to the bottom, wherein it is essentially the same distance from opposing points on the inside 17 opposite one another with respect to the central axis 12, i.e., running essentially at the center of the interior space 9. In the area of the preform body 21 connected to the neck part 31, the interior space 19 may optionally taper, wherein it reaches its smallest cross section in the area 27 of the bottom 23 of the preform 11. The inside 17 of the wall 13 in the area 27 just described is at a maximum distance of 3.5 millimeters from the central axis 12, wherein this area is adjacent to the bottom 23 of the preform 11 and is at least 30 millimeters long.

[0146] FIGS. 3a and 3b show, on the basis of the prior art, the problems in production of a plastic container from a preform 11 according to FIG. 1, which has a preform body with a small cross section.

[0147] In the known stretch blow molding process, it is provided that the stretching mandrel 51 does not come in contact with the preform 11 during the insertion of the stretching mandrel into the preform 11 until reaching the bottom thereof. FIG. 3a illustrates this desired situation, where it is shown that the stretching mandrel 51 is not in contact with the preform 11 except at its tip.

[0148] In contrast with that FIG. 3b illustrates the situation when the stretching mandrel 51 is inserted incorrectly, in which a lateral contact of the preform 11 leads to local cooling of same at the point of contact. The introduction starting on page 1 of this document explains how such a situation may come about and what the consequences are.

[0149] FIG. 2 shows an inventive embodiment variant in which the stretching mandrel 51, while it is being inserted into the preform 11 and before it reaches the bottom 23 (cf. FIG. 1) of the preform 11, comes in contact with the inside 17 (cf. FIG. 1) of the preform 11 in the area of the preform body 21 at several locations (such as at regular intervals) along its circumference or continuously along its circumference. This leads to a more uniform influence on the preform temperature and prevents the problems associated with FIG. 3b.

[0150] It can be seen on the basis of FIG. 1 that the preform body 21 extends along a central axis 12 of the preform 11, and the preform 11 has a wall 13 bordering an interior space 19 of the preform 11 and having an inside 17 and an outside 15. The stretching mandrel 11 extends along a central axis 52 of the stretching mandrel, wherein in the ideal case the central axis of the stretching mandrel essentially corresponds to the central axis 12 of the preform 11 during insertion into the preform 11.

[0151] Within an area 49 connected to the tip of stretching mandrel 51, the extent of the stretching mandrel 51 at a right angle to the central axis 52 of the stretching mandrel 51 is at least as large as the extent of the interior space of the preform 11 at a right angle to the central axis 12 of the preform 11 within an area 29 connected to the bottom of the preform 11. It is possible that this is true of the area 49 of the stretching mandrel and/or the area 29 of the preform over its entire length or only for one, two or more locations along the aforementioned areas 29, 49. The two aforementioned areas 29, 49 are not necessarily equal in length. It may be advantageous if said areas 29, 49 have a length of at least 5, 10 or 20 millimeters and/or at most 100, 80 or 70 millimeters. Unless otherwise indicated, directional information about the areas 29, 49 is based on a direction parallel to the respective central axis 12, 52. The area 29 described for the preform may correspond to the area 27 with a small cross section according to FIG. 1.

[0152] Due to the fact that the stretching mandrel may be designed to be thicker in relation to the dimensioning of the preform body, stretching mandrels of a sufficient stability may also be used for further processing of preforms with a small inside diameter.

[0153] FIG. 4 shows various types of stretching mandrels. The first stretching mandrel 51 from the left has a cylindrical stretching mandrel body while the second stretching mandrel 51 has a conical stretching mandrel body. The third and fourth illustrations show the same stretching mandrel 51, once in a side view and once in a sectional view along the central axis. This third variant of a stretching mandrel 51 is hollow on the inside and has openings 53 at the tip of the stretching mandrel leading into the hollow cavity. In the (main) blowing and/or in the optional preliminary blowing, the fluid can be introduced into the preform through the cavity and the openings 53.

[0154] It can be stated in general that suitable stretching mandrels 51 have a cross section (section at a right angle to the central axis of the stretching mandrel) or a (exterior) circumference of the stretching mandrel 51 such as that defined in the description, which may be round, oval or even polygonal (regular or irregular) with at least four, five or six corners, for example. It is also possible for the aforementioned cross section or circumference to have outwardly facing corners (away from the central axis) and/or inwardly facing corners (toward the central axis) and/or rounded edges. For example, said cross section or circumference may have a flower shape or the stretching mandrel 51 may have webs such as those mentioned in the description.