PREFORMS AND METHOD FOR PRODUCING PREFORMS

Abstract

The invention relates to a preform for producing a plastic container in a 2-stage stretch blow molding method, said preform having a preform body that extends along a central axis and that comprises: a first end a second end that lies opposite the first end, wherein the first end is closed and a neck part with a pouring opening adjoins the second end; and an inner wall that delimits an interior of the preform. Along a length of at least 30 mm of the interior, every point of the inner wall is at a distance of less than 3.5 mm from the central axis. Also disclosed are a suitable method and a device for producing such a preform.

Claims

1. A preform for producing a plastic container in a two-step injection stretch blow molding process, comprising: a preform body extending along a central axis thereof and having a first end and a second end opposite the first end, the first end being closed by a preform bottom; a neck part haying a pour opening connected to the second end of the preform body; and an inside wall bordering an interior space of the preform body, each point on the inside wall in the interior space being less than 3.5 mm away from the central axis for a length of at least 30 mm.

2. The preform of claim 1, wherein each point on the inside wall in the interior space is less than 3 mm or less than 2.5 mm away from the central axis for a length of at least 30 mm.

3. The preform according to of claim 1, wherein the preform body is comprised of polyester, the polyester being PEF or PET.

4. The preform of claim 1, wherein an (a)/(b) ratio is greater than 60 and less than 110, wherein (a) is an average wall thickness of the preform in an area of the preform body and (b) is a length corresponds to the wall of the preform from the pour opening to a midpoint of a preform bottom, wherein the length of the wall is measured along a line running in the area of the preform body at the center of the wall and running at a constant distance from the inside wall in an area of the neck part, wherein the constant distance corresponds to a distance from the inside wall in the center of the wall at a location of the smallest wall thickness.

5. The preform according to of claim 4, wherein the inside wall in the interior space in the area of the neck part is a distance of more than 4.5 mm up to 11 mm away from the central axis in at least a partial area.

6. The preform of claim 1, wherein the preform is for producing a plastic container with a capacity of less than 400 milliliters.

7. The preform of claim 1, wherein the preform has an acetaldehyde content of less than 2.5 ppm at an age of less than 6 months.

8. The preform according to claim 1, wherein the preform does not contain any acetaldehyde-reducing additives or any chain extender additives.

9. A method for producing a preform; comprising: completely filling a cavity of a mold with a hot molten polymer composition, wherein the cavity is formed by a female mold and a core, wherein the female mold defines an exterior shape of a preform and wherein the core defines a shape of an interior space of the preform in an area of a neck part; cooling the hot polymer composition by contact with the female mold and the core, wherein volume shrinkage of the polymer composition is induced by cooling the polymer composition; and inserting a pin into the polymer composition along a central axis of the preform to be produced, wherein due to the insertion of the pin the volume shrinkage is compensated, wherein the pin defines at least a partial area of the shape of the interior space of the preform in an area of the preform body, and wherein each point on the inside wall of the preform to be produced is a distance of less than 3.5 mm away from the central axis along a length of at least 30 mm; and removing the preform from the cavity, the preform comprising: a preform body extending along the central axis thereof and having a first end and a second end opposite the first end, the first end being closed by a preform bottom; the neck part having a pour opening connected to the second end of the preform body; and an inside wall bordering an interior space of the preform body, each point on the inside wall in the interior space being less than 3.5 mm away from the central axis for a length of at least 30 mm.

10. The method of claim 9, whereint each point on the inside wall of the preform to be produced is a distance of less than 3 mm or less than 2.5 mm away from the central axis along the length of at least 30 mm.

11. The method of claim 9, wherein a volume of the polymer composition in the cavity before insertion of the pin is greater than a volume of the polymer composition in a shape of a finished preform on removal of the preform from the cavity.

12. The method of claim 9, wherein an the amount of polymer in the polymer composition in the cavity before insertion of the pin is equal to an amount of polymer in the polymer composition in a shape of the finished preform on removal of the preform from the cavity.

13. The method of claim 9, further comprising finishing the preform by injection molding without holding pressure from an injection machine used for the injection molding.

14. The method of claim 9, wherein during the insertion of the pin into the polymer composition, a portion of the pin that comes in contact with the polymer composition is not cooled.

15. The method of claim 9, further comprising cooling the pin from an outside thereof before inserting the pin, by contact with the core, wherein the core is cooled by a coolant flowing through a plurality of cooling ducts.

16. The method of claim 9, further comprising applying a lubricant film to a surface of the pin in the form of one of a wax-based, oil-based or a soap-based lubricant coating.

17. The method according to of claim 9, further comprising producing the preform by injection molding, wherein an average dwell time of the polymer composition in an injection machine used for the injection molding is less than 50 seconds and the temperature in the injection machine is more than 250 C., wherein the polymer composition does not contain any acetaldehyde-reducing additives.

18. The method according of claim 9, further comprising producing the preform produced by injection molding, wherein by adjusting the average dwell time of the polymer composition in the injection machine used for the injection molding and by adjusting the temperature in the injection machine, the decline in viscosity of the polymer composition in the injection machine is kept below 0.02 dL/g, measured according to ASTM D4603, wherein no chain extender additives are added to the polymer composition.

19. A device for producing a preform, comprising: a mold with a cavity, wherein the cavity is formed by a female mold and a core; the female mold is designed to define an exterior shape of the preform, the core is designed to define a shape of an interior space of the preform in an area of the neck part; a pin that can be inserted from the core into the cavity along a central axis of the preform to be produced; the pin designed to define at least a partial area of the shape of the interior space of the preform in an area of the preform body, wherein each point on the pin is a distance of less than 3.5 millimeters away from the central axis of the preform to be produced along a length of at least 30 millimeters the preform comprising: a preform body extending along a central axis thereof and having a first end and a second end opposite the first end, the first end being closed by a preform bottom; a neck part having a pour opening connected to the second end of the preform body; and an inside wall bordering an interior space of the preform body, each point on the inside wall in the interior space being less than 3.5 mm away from the central axis for a length of at least 30 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0145] In schematic diagrams, not drawn to scale:

[0146] FIG. 1a: shows a sectional diagram of parts of a machine for production of a preform with the pin not yet inserted;

[0147] FIG. 1b: shows a diagram like that in FIG. 1 with the pin inserted; and

[0148] FIG. 2: shows a sectional diagram of a preform.

EMBODIMENT OF THE INVENTION

[0149] The invention is described below as an example on the basis of the figures.

[0150] FIGS. 1a and 1b show device parts of a machine for producing a preform, while FIG. 2 shows a preform that can be produced using such a machine.

[0151] With reference to FIG. 2, the preform 11 has a preform body 21 and a neck part 31 connected to it. 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 and forms a bottom of the preform 11. The neck part 31 has a pour opening 35 and is connected to the second end 25 of the preform body 21. In 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 30, 40 or 50 millimeters.

[0152] Additional advantageous features of the preform 11 include, as shown in FIG. 2, a thread 37 and a supporting ring 39 on the neck part 31. The thread 37 allows subsequent attachment of a cover (not shown) to the pour opening of the plastic container to be produced from the preform 11. The supporting ring 39 facilitates handling of the preform 11, which brings advantages in particular in the case of a two-step injection stretch blow molding process such as that provided for production of the preform 11 and of the plastic container (from the preform). In such a two-step process, the preform 11 is cooled to room temperature after being produced and only later is processed further to form a plastic container in a stretch blow molding process. The preform 11 is produced in one piece by injection molding from a polymer such as polyester, wherein this may also applicable to structures such as 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 35 has the pour opening. The latter leads into the interior space 19 of the hollow preform 11, wherein the interior space 19 extends from the pour opening to the bottom of the preform 11. The interior space 19 is bordered by the inside 17 (i.e., the internal surface) of the wall 13 which also has an exterior side 15 (i.e., an outer surface). The distance between the inside 17 and the outside 15 is the wall thickness, which may be larger 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, may be disregarded in evaluating the wall thickness. The wall thickness in the area of the neck part may advantageously be 0.5 to 3 millimeters. In the area of the preform body, the wall thickness may be 2 to 8 millimeters. In the production of the plastic container from the preform 11, only the preform body 21 is normally stretched and blow molded. The interior space 19 has a larger cross section in the area of the neck part 31 than in the area of the preform body 21, wherein the term 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 pour opening to the bottom, wherein they are essentially the same distance away from one another with respect to the points on the inside 17 opposite the central axis 12, i.e., running in the center of the interior space 19. In the area of the preform body 21 adjacent to the neck part 31, the interior space 19 tapers, reaching its smallest cross section in the area 27 of the first end 23 of the preform body 21. The inside 17 of the wall 13 is a distance of max. 3.5 millimeters from the central axis 12 in the area 27 just described, wherein this area is connected to the bottom of the preform 11 and is at least 30 millimeters long.

[0153] A preform 11 that is suitable for a two-step injection stretch blow molding process may have a circular cylindrical section of the preform body 21 extending in the direction of the bottom 23 of the preform, as shown in FIG. 2, adjacent to a bottom side of the supporting ring 39 facing away from the pour opening 35, the wall thickness of this cylindrical section being smaller than the wall thickness of a section of the preform body 21 connected to the bottom 23 of the preform. Typical wall thicknesses of the circular cylindrical section may be between 1 mm and 2.5 mm. A section of the preform body 21 which is usually conical and tapers in the direction of the bottom 23 of the preform, also referred to as the preform ramp or preform shoulder, and connects the circular cylindrical section to the section of the preform body 21 connected to the bottom 23 of the preform. The wall thickness of the conical section usually increases successively from the wall thickness of the circular cylindrical section to the wall thickness of the section of the preform body connected to the bottom 23 of the preform. Alternatively, as shown in FIG. 2, the wall thickness of the conical section may remain approximately constant, wherein the wall thickness of the preform body 21 then becomes larger only in the section of the preform body 21 connected to the bottom 23 of the preform, as may be the case with preforms having stepped preform bodies. Typical wall thicknesses of the section of the preform body 21 connected to the bottom 23 of the preform are 3 mm to 5 mm.

[0154] With regard to the production of the preform 11 described above, reference is made to FIGS. 1a and 1b where parts of the device suitable for this task are shown. The preform 11 from FIG. 2 can also be seen in FIG. 1b (cf. reference numeral 20). When mentioning parts of the preform 11, reference is also made supplementally to FIG. 2.

[0155] The preform 11 is produced by injection molding from a polymer composition 20. To do so, an injection mold having a cavity 51 is required, wherein the shape of the cavity 51 defines the shape of the preform 11 to be produced. The polymer composition 20 is produced by injection molding into the cavity 21 at a sprue point 65, wherein the cavity 51 is filled completely with the polymer composition 20. During the injection, the cavity 51 is formed by a female mold (not shown) and core 61 wherein the female mold defines the shape of the entire outside 15 of the wall 13 of the preform 11 to be produced and wherein the core 51 defines the shape of the inside 17 of the wall 13 of the preform 11 to be produced in the area of the neck part 31. Due to the contact with the cooled female mold and the cooled core 61, there is a drop in the temperature of the polymer composition 20, which is still above the melting point of the polymer composition 20 on entrance into the cavity 51. Volume shrinkage occurs due to the cooling of the polymer composition 20, i.e., the polymer composition 20 shrinks. The volume thereby freed up in the cavity 51 that was previously completely full is filled by a pin 71 that is inserted through an opening 63 from the core 61 into the cavity 51. While the pin 71 is in the core 21 that is cooled, it is cooled from the outside due to the direct contact with the cooled core 21. However, it does not have any cooling ducts itself. Since the polymer composition 20 cools from the outside to the inside, it is still molten at the location where the pin 71 is inserted into the polymer composition 20. The pin 71 presses the polymer composition 20 against the female mold when it is being inserted and thereby prevents the polymer composition from separating from the mold. The pin 71 thus inserted into the cavity 51 alters the shape of the cavity 51 and defines the shape of the inside 17 of the wall 13 of the preform 11 in an area 27 of the preform body 21, wherein the tip 73 of the pin 71 defines the shape of the inside 17 of the bottom of the preform 11. The aforementioned area 27 is a partial area at least 30 millimeters long, connected to the inside 17 of the bottom of the preform 11. Since the pin 71 is only inserted when the polymer composition 20 is already in the cavity 51, the polymer composition 20 must not flow around the pin 71 during injection. Instead of a narrow annular channel between the pin and the female mold, the polymer composition 20 has only a limited channel through the female mold from the injection point 64 until reaching the core 61 for distribution in the cavity 51. This prevents the polymer composition 20 from cooling too rapidly and thus increases the flexibility with regard to the dimensioning of the preform. When the pin 71 has been completely inserted into the cavity 51 (i.e., until reaching its intended end position), the shape of the cavity 51 corresponds to the shape of the preform 11 to be produced. The polymer composition 20 cools in the cavity 51 down to below the glass transition temperature and solidifies. The resulting preform 11 may then be removed from the cavity 51.