PLASTIC CONTAINER

Abstract

The invention relates to a plastic container which is stretch blow-molded from a preform and which comprises a container body having a container neck attached thereto, on which container neck there is provided an outlet opening, wherein the container body has a second opening closed by a weld seam. The container is made from a copolyester. The wall of the stretched container body has a stretching ratio relative to the wall of the unstretched container neck in the region of the at least one weld seam of more than 6:1. After the welding, the stretched container body has a density increase relative to the unstretched container neck in the region of the at least one weld seam of less than 0.06 g/cm.sup.3.

Claims

1. A copolyester container that is stretch blow-molded from a preform comprising: a stretched container body having a container neck attached thereto, the container neck having an outlet opening, and the container body having a second opening closed by a weld seam; a container wall of the stretched container body having a stretching ratio relative to a neck wall of the unstretched container neck in a region of the weld seam of more than 6:1; and the stretched container body having greater density relative to the unstretched container neck in the region of the weld seam of less than 0.06 g/cm.sup.3 after welding.

2. The container according to claim 1, wherein the copolyester of the container is polyethylene terephthalate (PET) having a copolymer content between 4 wt. % and 10 wt. %, and the copolymer comprises isophthalic acid, diethylene glycol, furan dicarboxylic acid, propylene glycol, or butylene glycol.

3. The container according to claim 1, wherein the copolyester of the container is polyethylene furanoate (PEF) having a copolymer content below 5 wt. %, wherein the copolymer is terephthalic acid, isophthalic acid or diethylene glycol, propylene glycol, spiroglycol or butylene glycol.

4. The container according to claim 1, wherein the stretched container body exhibits a density increase relative to the unstretched container neck of less than 0.03 g/cm.sup.3 in the region of the at least one weld seam prior to welding.

5. The container according to claim 1, wherein the container comprises a tube having a tube neck and a tube end opposite the tube neck, wherein the outlet opening is situated in a region of the tube neck and the second opening is situated in a region of the tube end and the second opening is sealed by the weld seam.

6. The container according to claim 1, wherein the container comprises an integral handle formed with a reach-through opening, wherein the weld seam bounds off the reach-through opening by joining a first and second wall end bordering on the reach-through opening.

7. The container according to claim 1, wherein the weld seam has a length of 5 mm and is configured to withstand a tensile force of at least 100 N, the tensile force being oriented substantially perpendicular to the weld seam.

8. The container according to claim 1, wherein the container is comprised of a single layer for easier recycling.

9. The container according to claim 1, wherein the PET or the PEF of the container is bio-based in a proportion of at least 30% or produced from as much as 30% regenerate.

10. The container according to claim 2, wherein the second opening of the container that is closed by forming the weld seam in a temperature range that is above the glass temperature (T.sub.G) and below the melting temperature (T.sub.M) of the copolymer.

11. A method of manufacturing a plastic container from a preform formed from copolyester, comprising: stretch blow-molding the preform to form a container having a container body with a container neck attached thereto, the container neck having an outlet opening, wherein walls of the preform are stretched respectively by at least 6 times relative to an unstretched state at least in a region where a weld seam is produced and a density of the walls in a stretched region is increased by at most 0.03 g/cm.sup.3, pressing together the stretched walls, and welding the stretched walls together to form a weld seam at a welding temperature between a glass transition temperature (T.sub.G) and a melting temperature (T.sub.M) of the copolyester.

12. The method according to claim 11, further comprising increasing the density of the walls in the region of the weld seam by at most 0.06 g/cm.sup.3 due to the welding.

13. The method according to claim 11, further comprising forming an integral handle with a reach-through opening on the container, the weld seam bounding off the reach-through opening by joining together walls bordering on the reach-through opening.

14. The method according to claim 11, further comprising severing or cutting off a portion of the container prior to the pressing together and welding together, thereby producing an opening, the opening closed during the forming of the weld seam at a welding temperature between the glass transition temperature and the melting temperature of the copolyester.

15. The method according to claim 11, wherein a welding time during which the walls are held at welding temperature is between 1 and 6 seconds.

16. The method according to claim 11, further comprising welding the walls together between a first and a second welding jaw, a pressing force against the walls being between 50 and 50000 N/cm2.

17. The method according to claim 16, further comprising opening the welding jaws at a cooldown temperature, the cooldown temperature being below the glass transition temperature.

18. The method according to claim 11, wherein the copolyester is polyethylene terephthalate (PET) having a copolymer content between 4 wt. % and 10 wt. %.

19. The method according to claim 11, wherein the copolyester is polyethylene furanoate (PEF) having a copolymer content below 5 wt. %.

20. The method according to claim 1, further comprising stretch blow-molding the preform in a blow mold for producing a tube, stripping the tube from the mold, cutting off a closed tube end opposite a neck of the tube, the tube configured to be filled with contents through the second opening, and the second opening closed by welding.

21. The method according to claim 11, further comprising producing a junction between stretched walls of the plastic container.

22. A use of a copolyester for production of a preform in order to manufacture a container from the preform in a stretch blow-molding process, wherein the container comprises a container body and a container neck attached thereto, having an outlet opening, and wherein the container has a second opening closed by a weld seam, the copolyester is polyethylene terephthalate (PET) having a copolymer content between 4 wt. % and 10 wt. %, or polyethylene furanoate (PEF) having a copolymer content below 5 wt. %.

23. The use according to claim 22, wherein a surface of the container in a region of the weld seam has a stretching ratio relative to the surface of the preform of more than 6:1 and the container body after the welding has a density increase in a region of the weld seam of less than 0.06 g/cm.sup.3 relative to the preform body.

24. The use according to claim 22, wherein the copolyester is polyethylene terephthalate (PET) having a copolymer content between 4 wt. % and 10 wt. %, and wherein the copolymer is isophthalic acid, diethylene glycol, furan dicarboxylic acid, propylene glycol, or butylene glycol.

25. The use according to claim 22, wherein the copolyester is polyethylene furanoate (PEF) having a copolymer content below 5 wt. %, and wherein the copolymer is terephthalic acid, isophthalic acid or diethylene glycol, propylene glycol, spiroglycol, or butylene glycol.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Further advantages and features will emerge from the following description of two exemplary embodiments of the invention, making reference to the schematic representations. There are shown, not being drawn true to scale, in:

[0048] FIG. 1: 4 method steps of producing a tube from a preform;

[0049] FIG. 2: a representation of the producing of a plastic container with handle from a preform;

[0050] FIG. 3: a representation of a first sample type for determining the tensile strength of a weld seam on a plastic container, and

[0051] FIG. 4: a representation of a second sample type for determining the tensile strength of a weld seam on a plastic container.

DETAILED DESCRIPTION OF THE INVENTION

[0052] The present invention relates to a plastic container. The plastic container is a tube 11 or a container (handle container 13) having an integrally formed handle 15. The container has at least one weld seam 17 and is stretch blow-molded from a preform 19. The plastic container (tube 11, handle container 13) comprises a container body 21 and a container neck 23 adjacent to the container body 21. The container body 21 has a wall 25 enclosing a cavity 27. The container neck encloses an outlet opening 29. Through the outlet opening 29, the contents placed in the plastic container can be removed.

[0053] The invention makes it possible, in surprising manner, for a first and a second wall end 39a, 39b or a second opening 40 of the container to be sufficiently firmly weldable, so that the weld seam 17 passes the prescribed strength tests. This is so even though the container is produced according to a standard stretch blow-molding process from a preform 19 and consists of a copolyester. In this way, it is possible to stretch blow-mold a tube 11 or a handle container 13 from a preform, consisting of PET or PEF, the wall ends of which need to be welded or a second opening needs to be welded.

[0054] In the standard stretching process, the preform 19 is placed in a blow mold 31, the container neck 23 remaining outside the blow mold 31. The preform 19 comprises a preform body 20 and a preform neck 22. The preform is usually heated to the required processing temperature before being placed in the blow mold 31. Through the outlet opening 29, a blowing lance is introduced into the preform 19, stretching the preform 19 by a particular amount in the axial direction. The preform is then blown with a gas, which is blown in through the blowing lance, and further stretched radially and axially, until the wall 25 lies against the blow mold 31. After the cooldown of the produced container, it can be removed from the blow mold 31. The container neck 31 may also have an external thread 33, by which a closure cap having a corresponding internal thread can be screwed onto the container neck 23.

[0055] In order to connect the wall ends 39a, 39b by a weld seam 17, or to close the second opening 40 by the weld seam 17, the stretch blow-molded material of the container must have certain properties. Otherwise, the weld seam 17 might not fulfill the strength requirements, especially those involving a container in which foodstuffs are packaged.

[0056] The first and the second wall end can be welded between the glass transition temperature T.sub.G and the melting temperature T.sub.M of the copolyester. Below the glass transition temperature, no welded connections can be produced, since these temperatures are too low. Above the melting temperature, the strength properties achieved by the stretching of the preform 19 are lost. This includes the lost stretch crystallization. Furthermore, the weld seam 17 after the heating above T.sub.M cools down to crystallize either amorphously or spherulitically. In either case, such a crystallized PET is more fragile than stretched PET and therefore it is unsuitable for a flexible packaging. By stretch crystallization is meant that the stretching can bring molecules so close to each other that they can bring about intermolecular interactions with each other. These interactions are responsible for an adhesion between the molecules, making the container stronger, more flexible, and more tough. A welding of copolyesters is possible above the glass transition temperature, since molecular entanglements or adhesions with molecules between the partly crystalline zones may form as a result of the chain mobility occurring in this temperature range.

[0057] The welding of the copolyester in the above specified temperature range results in a sufficiently firm weld seam 17 when the wall of the container body has been stretched by at least 6 times relative to the wall of the preform body 20. It is understood that this stretching ratio must be present in particular in the region of the weld seam 17.

[0058] In order for the weld seam 17 to have a sufficient stability after the cooldown, the stretch crystallization in the region of the weld seam 17 should not be more than 20% prior to the welding. In combination with the welding conditions defined further below, one can prevent the material of the weld seam from having a crystallization of more than 40% and becoming fragile. This can be achieved in that the proportion of copolymers in the copolyester has a certain value. For PET, it has been found that the proportion of the copolymers between 4 wt. % and 10 wt. % is especially suitable for keeping the crystallization (the degree of crystallization) low. For PEF, the proportion of less than 5 wt. % of copolymers is especially suitable.

[0059] Since the crystallization is idealized from 0% to 100%, in the context of this application the values for the density increase are indicated in place of the crystallization, since a heightened crystallization goes hand in hand with an increased density. The density of the preform body 20 will be compared to the density of the container body 21 or that of the unstretched container neck 23. A crystallization of 20% corresponds to a density increase of the container body by 0.03 g/cm.sup.3 as compared to the preform body 20 or the unstretched container neck 23. That is, the density of the container body 21 without the container neck 23 has increased by 0.03 g/cm.sup.3 as compared to the density of the preform body 20 without the preform neck 23. A crystallization of 40%, which the material of the weld seam falls short of, corresponds to a density increase of 0.06 g/cm.sup.3 as compared to the preform body 20 or the unstretched container neck 23.

[0060] In order to determine the optimal welding conditions for producing a durable and nonbrittle weld seam 17, wall samples 35 are cut out from the wall 25 of the stretched container body 21. The sample 35 has a width of 12 mm at its opposite ends. In the middle of the sample 35, the width narrows to 5 mm. The sample 35 therefore has the shape of a bone. In the middle of the sample, the sample is cut apart across its lengthwise dimension. The two resulting sample pieces are joined together again with a weld seam 17. The parameters for producing the weld seam are varied in order to optimize the strength of the weld seam 17. Besides the duration of the welding time .sub.s, the value of the welding temperature T.sub.s and the cooldown temperature T.sub.C, the nature of the weld seam is also varied. FIG. 3 shows a butt type weld seam 17, while FIG. 4 shows an overlapping weld seam 17. The butt-type weld seam has a maximum peeling stress and the overlapping weld seam has a maximum shear stress.

[0061] After producing the weld seam 17, the wall sample 35 is subjected to a tensile test, the ends being clamped in a tensioning device. The weld seam is oriented 90 degrees +/−5 degrees toward the tensioning direction. Both the butt type and the overlapping weld seam 17 are sufficiently strong when sustaining 100 N of tensile force. The tensile force was applied to the wall sample by the tensioning device with a longitudinal speed of 100 mm/min.

[0062] As already mentioned further above, a welding temperature T.sub.S results in a sufficient strength of the weld seam 17, being between the glass transition temperature T.sub.G and the melting temperature T.sub.M. For PET copolymers, this temperature range is between 170° C. and 220° C. For PEF and PEF copolymers, this temperature range is between 120° C. and 210° C. A sealing time t.sub.S of 3 seconds, being the time when the welding jaws weld together the first and second wall end with the sealing temperature T.sub.S, proves to be optimal. The cooldown temperature T.sub.C at which the welding jaws are opened once more is below T.sub.G. The pressing force of the welding jaws against the first and second wall ends is between 50 and 50000 N/cm.sup.2.

[0063] FIG. 1 shows the production of the tube 11 from the preform 19. The preform is placed in the blow mold, with the preform neck 22 remaining outside the blow mold. After stretching, blowing, and removal of the resulting plastic container, as already described further above, the container has a bottom or a tube end 37, which is no longer needed. The tube end 37 is cut off and can therefore also be considered to be a “lost” tube end. There are formed a first and second wall end 39a, 39b, which need to be permanently joined together by the weld seam 17, or the second opening 40 needs to be closed by the weld seam 17. Typically, the tube 11 can be filled with contents prior to the closure by the weld seam 17. The lost tube end is generally recycled within the production operation.

[0064] The weld seam 17 is produced according to the above welding parameters. Stress tests have shown that the weld seam 17 can sustain a dropping of the tube 11 onto the weld seam from a height of 2 m. After 20 repetitions of bending of the weld seam 17 across a pipe with a diameter of 30 mm, the weld seam 17 still remains tight. A kinking of the weld seam does not result in any leakage of the weld seam, either. Such a tube 11 therefore fulfills the stress requirements which must be met by tubes of the prior art.

[0065] FIG. 2 shows the production of the handle container 13 from the preform 19. After producing a container by the standard stretch blowing process, as described further above, a reach-through opening 41 is cut or punched out from the container. This produces a first and second wall end, which surround the reach-through opening or a second opening. In order to seal the handle container once more along the reach-through opening, the first and the second wall end must be welded together to form the weld seam 17 or the second opening must be closed. In order for the weld seam 17 to be sufficiently stable, this is produced by obeying the above specified welding parameters.